Tough to say, you should experiment. So long as the starter doesn't kickback, the initial timing isn't all that critical. What will usually happen though, a stock OEM distributor is "lazy" and has a slow and conservative timing curve. Especially heavy vehicles like trucks. Consequently if bumping it up there to 18° BTDC, there will now be way too much advance on the far side, at higher RPM, under full acceleration. If wanting to run higher initial timing degrees like that it's pretty much required to get in the distributor and limit the amount of centrifugal advance. The "total" timing, that is initial + centrifugal, in degrees, doesn't change but you can run more initial timing, by limiting the centrifugal.

Make sure the distributor itself is working correctly all through the RPM ranges. They get old, they get loose. The precision drops way off, and engine will rattle and ping even without excessive advance, requiring you to detune your engine to compensate. Also make sure the vacuum advance is working correctly. This allows engine to run smoother and cooler and will improve efficiency, especially on highway trips. Definitely will see improved efficiency and better performance by optomizing the overall ignition timing. Couple that with some careful carburetor tuning and it will be pretty respectable vehicle range or fuel mileage, at least as far a heavy vehicle with really bad aerodynamics is concerned. Keep a close eye on plugs, it's very hard to read plugs with modern fuel, and you may need to drop a heat range when running advanced timing.

Yes, Ford used that type of reluctor for a long time. There are different "slots" available depending on the application. 13L or 18L are two common flavors. Distributor degrees are half of actual crankshaft degrees, so a 13L slot equals 26° timing (at high RPM) + whatever the initial timing is set at. An 18L slot equals 36° on the damper - way too much advance to run 18° initial! This is what I was referring to earlier. For lighter weight cars and some more pep, a lot of guys will limit the distributor advance inside to, or look for, say a 10L slot. These are harder to find. Part of the problem is rebuilt distributors are like a box of chocolates, "never know what you're gonna get". Maybe it originally came out of a Torino or, maybe a Dumptruck, who knows. It might be totally unsuitable for your application until you recurve it. So you really need to check and get a handle on exactly what the distributor is doing.

Also the springs are just as important. Lighter weight springs allow the advance to come earlier RPM, this might be a big part of your complaint as far as power is concerned. Usually the stock or OEM truck springs are pretty stout, with at least one super heavy secondary spring. Sometimes the maximum mechanical advance won't be "all in" till better than 4000 RPM in trucks. Experimenting with these, maybe two medium springs, maybe one light, one medium, two light springs, etc, will get something better for you. Mr. Gasket 925D will get a kit of 2 lighter springs to mess with.

Keep in mind if you want to use your truck as a truck and haul heavy loads, dialing in a lot of timing, and dialing it in real early would not necessarily be a good plan. Another tuning aid, the two posts that the springs mount to can be bent or tweaked slightly to loosen or tighten the tension on the springs. This will cause the centrifugal advance to come in a little earlier, or a little later, for fine tuning the curve. The advance plate if you look carefully has an access hole that lines up with the posts for adjustment without removing the distributor or disassembling. It's tedious to do all this stuff but it's the only way to get it dialed in unless you've a distributor machine or want to pay someone to do it for you.

Disconnect and plug the vacuum advance. Forget it even exists for a while while tuning the distributor itself, experiment with different spring weights & combinations and see how much the engine likes in terms of more (or less) initial timing + centrifugal advance combinations. Check for knock on heavy acceleration.

I wouldn't worry too much about the absolute timing numbers, see what your engine combo likes. This will take some test drives and on the fly adjustments. Then, when you get it dialed in, and like how it runs don't mess with it again; re-connect the vacuum advance, and tune only the vacuum advance timing canister.

Vacuum advance mostly just rides on top of whatever the centrifugal is doing, pulling in even more timing when engine load is low, and reverting back to centrifugal advance numbers when engine load is high. A common error is to retard the distributor timing to cure engine knock or pinging, when the problem is simply the vacuum advance pulling in way too much. Don't do this. Experiment here too, and see which kind of combination nets better mileage.

Limiting the total internal centrifugal advance to a smaller value than stock gives more "room" to experiment than otherwise would be possible, including high initial timing settings like you mentioned without busting the far end. Or can try using the lower initial timing settings and higher vacuum advance settings. The total timing numbers don't really change, just when. It can be rewarding to do this, it's all done by computers now, instead of steampunk valves, weights and springs.

Vacuum is measured by "inches of mercury" or in or ". But we know what you meant of course. The old school publications going way back suggested the optimum point when timing using manifold vacuum as a signal to be just short of the maximum steady vacuum achieved, and then backing off only slightly by about 1/2". This is for pump gas. A stock or OEM distributor curve may not allow that much lead though unless you get in the distributor and limit the far side. In practice that's what most people without a gauge or even a light end up doing, advancing till it pings on hard acceleration and backing off, because they don't want to get inside the distributor much less buy a timing light.

Here is some old school techniques, from a late 1940s
"Hygrade Tune-Up & Carburetor Manual"

https://www.carbkitsource.com/tech/articles/TuneUp/CarburetorTuneUp01.html

VACUUM GAUGE

TESTS WHILE ENGINE IS RUNNING

For a normal idle, with throttle stop screw adjusted for a minimum of 7 miles per hour in high gear, the hand of Vacuum Gauge should register between 18" and 21" while engine idles. In setting the carburetor idle point with Vacuum gauge, best results are obtained by first jacking up the rear wheels one inch from the floor, starting the engine and putting the transmission into high gear, then adjusting the throttle stop screw until speedometer indicates 7 miles per hour minimum. DO NOT attempt to adjust IDLE AIR NEEDLE or SCREW until minimum speed has been set. Adjust hand close to one full turn out from seat until highest reading is indicated. When certain that highest reading has been obtained, check speedometer again. If there is a higher or lower reading than 7 miles per hour, reset the throttle stop screw for the 7 M.P.H. minimum. THIS IS VERY IMPORTANT.

SPECIAL NOTE: On automatic transmissions, the idle stop screw adjustment should be made with an electric Tachometer for specification set up for the individual job.

After proper engine idle speed, and approximately correct idle mixture is attained, accelerate engine by quickly lifting throttle arm and releasing it. The Vacuum Gauge hand should drop to 2" and recoil to 24" or more. If the recoil is not more than 24", there is indication of very well diluted oil in the crankcase or poorly sealing piston rings.

Next, run engine to about 30 M.P.H., and hold throttle steady. The hand should at first fall back, then gradually climb up to its peak. Reading should now be from 1" to 2" higher than idling reading. If it isn't, the automatic advance mechanism is not functioning properly, or at all. If it does advance, the advance mechanism is working satisfactorily.

When the throttle is opened to 30 M.P.H., or more and held steadily, if the hand of Vacuum Gauge fluctuates rapidly between 10" and 21" or 22", it is an indication that the valve springs are weak, and not closing the valves as they should. As the engine speed is increased, the fluctuations become more rapid.

LOOSE BOOSTER BRAKE CONNECTIONS CAUSES LEAN MIXTURES AND LOWER BRAKE POWER EFFICIENCY.

CORRECT SETTING OF IGNITION TIMING WITH VACUUM GAUGE

Connect gauge to intake manifold. Start engine after jacking up rear wheels just off floor. Set throttle stop screw until speedometer shows 14 to 15 M.P.H., no more. Hook up Vacuum Gauge on distributor side for convenience, loosen distributor lock plate screw. While watching Gauge, turn distributor body whichever way it has to go for retard, until hand indicates 16" or 17". Then, turn distributor body in opposite direction to advance until hand reaches its highest point and begins to fluctuate ahead. Hold it at this point for an instant, then turn distributor body back again very easy, just enough to remove the bounce or fluctuation, thus causing the hand to remain perfectly steady. This is the best point of setting. Lock distributor plate lock screw on side. This allows very close ignition timing setting without "ping" or knock. A road test will then definitely prove the setting is correct.

If the motor is in perfect condition, the hand of Vacuum Gauge will remain steady between 15" and 21".

Altitude has a definite effect on Gauge readings.

At sea level, the Gauge will read approximately 19.5".

For each 1,000 feet above sea level, the Gauge will drop one inch.

Example:
At 2,000 feet the Gauge will read approximately 17.5".
At 5,000 feet it will be 14.5", and at 10,000 feet it will be 9.5".

Most carb manuals suggest turning them in slowly, 1/4 turn at a time, to keep them evenly adjusted. The idea overall is to have the idle mixture just right for smooth running. Very slightly rich, but not too much or plugs will tend to load up and foul. Should notice a definite point where the motor starts to stumble and RPM drops off. Backed out a 1/4 turn from there should be right in there for most weather conditions. When emissions testing came about it got a lot more complicated to get things to pass. What I noticed is there's kind of a time window to get it done, it does no good to spend 15 minutes or half hour dinking around to get it just right. As it sits there idling the plugs will start to load up, among other things. When it's good and warmed up, after a highway run say, don't dally and spend about 5 minutes right after you get back with your Golden Screwdriver and then leave it alone. Blip throttle to clear carb out between adjustments. Again the idea is to be just slightly rich, overall idle mixtures are pretty lean, to keep plugs from fouling up. Some people believe once spark plugs foul they never really come back, there might be some truth to that.

Everything was kind of a compromise in those days. Plugs had to be hot enough not to foul out at idle or driving around town in the winter, though not nuke themselves in the summer on the highway. So I adjust the carb a little richer in the winter and lean it pretty good in the summer. You can see how precise the screws are with a wideband O2 sensor hooked up. 1/8 of a turn on a single screw will make no noticeable difference in how it sounds, but the AFR will move a whole point. Somebody used to sell a clear glass spark plug called Gunson Colortune, when the idle mixture was just right, the flame would be blue instead of yellow. I think they are still around.