The belt on the truck says: GATES TRUCK & BUS 64 MADE IN USA N3
My issue is there is no modern GATES 64 belt and I cannot find a cross reference, but it is the perfect length.
I measured the outside circumference is 54 11/16. I might be off by a 1/16 and it's really 54 3/4?

I bought the Gates TR20544 because that is what OReilly's lists. RockAuto says the belt is TR20544.
The TR20544 is way too short. Even with the bolts on the generator loosened and pushed the bracket all the way down, there is no way the Gates TR20544 is getting on.
Yet Gates lists this belt as being "Outside Circumference (in) 54.82"

I saw this post with someone running a 5L570, so I bought that belt from Amazon and it's way too long. When I raise the generator up on it's bracket I max out the height and the belt is still loose.
https://www.jalopyjournal.com/forum/...-help.1030842/

I am looking for advice on a belt that is maybe 55"?
I would also love advice on how to properly tighten the belt. What is your anchor point and method?
I have a long breaker bar I am resting on the generator bracket bolt and prying up on it under the body of the generator. There has to be a better way.

 

I can't tell you what belt you need, but I can describe my method for tightening the two belts on the post-war flatheads. Disclaimer, I am still young enough that this works for me (I'm 40 and my back is still ok), I don't know how well it will work when I'm very "experienced".
1) Have the fan bolts really loose, and the generator nut just loose enough to easily slide the generator up and down. Have your 7/8 box end wrench close where you can grab it with one hand.
2) Lean over the radiator (I stand on the front bumper on most trucks) and pull up on the generator by hand. Make SURE the generator is lined up with the slot in the intake or you can break the sides of the intake slot. I pull up hard on the middle / back of the generator making sure the pulley is tight on the belt and the generator is leaning forward a bit.
3) Keep holding the back of the generator with one hand, grab your 7/8 wrench, and tighten the generator nut. When this works the generator belt will be tight enough, occasionally too tight. Usually the generator tilting back while tightening the nut will make the belt tighter.
4) Make sure that annoying square washer is lined up for your fan bracket and make sure your wrench for the fan bolts is close where you can grab it.
5) Pull up on the fan bracket, not the fan, making sure the square washer and fan bracket all line up with the generator. Frequently I will use my left hand to grip between the intake / generator retaining stud and the fan bracket.
6) Keeping tension on the fan belt tighten the fan bolts.

When this all goes well I can tighten both belts in less than a couple minutes. Also, for those new to old car wide fan belts, they are run much looser than serpentine belts. If you make these belts "fiddle string tight" you will damage something. Dad once sold a 39 sedan to a guy who though the fan belt was much too loose. The guy tightened the belt until a pulley broke and was pulled into the NOS radiator.

 

The Parts book shows a couple of different length belts, depending which generator sheave is used. See below. The 54.5" belt is likely what you have now, stretched a bit.

38 Coupe's procedure is about what I use, with a couple tricks. I take the fan belt completely off, and slide the fan bracket up to hold the square washer in place, then tighten that bracket. Tighten the gen/WP belt, then drop the fan bracket down to do that belt.

Usually you can also slip a screwdriver between the gen bracket and the intake manifold, from the front, to lever the gen up. But as said, don't over-tighten. Ditto on making real sure the gen bracket is in the guide before tightening.

 

My generator belt is a Gates Green Stripe TR20544 also has 15A1380 on it. The water pump belt is TR26366 and 20A0935. These are the wide belts.

 

I would like to thank everyone that replied, your ideas and guidance was appreciated.
I ordered a B52 belt through Grainger Supply and picked it up same day.
https://www.grainger.com/product/DAY...2-V-Belt-6X874

I was able to loosen the generator 7/8" bolt and slide the bracket down.
I then removed the 9/16" bolt from the strap holding the generator so I could tip it down. This allowed me to replace the belt.
I re-attached the generator strap and secured the 9/16" bolt.
I then slid some long needle nose pliers in between the 7/8" bolt and the underside of the generator. I used this because they are wedge shaped and a thin enough profile to fit in the space available.
Since they are long I can then use them as a fulcrum to push the generator tight.
While pushing with one hand I have the other free to tighten the 7/8" bolt.

For the fan belt I loosen both 5/8" bolts.
I then used a breaker bar to press up underneath the bracket against the block, just behind the driver's side water pump.
While pressing on the breaker bar with one hand, I am able to tighten one of the 5/8" fan belt bracket bolts.
I can then move to the passenger side and tighten that 5/8" bolt as well.

 

I've been using a B-51 Industrial belt on my pickup for several years since they were usually less expensive than the Automotive belt. I needed to replace mine in August and found a bargain on them at Amazon.


I was worried a bit about the quality, but when it arrived it looked and fit just fine. I may have the smaller generator sheave, and it was a fairly snug fit. I don't know if they offer a B-52 belt, or not. They're actually close to $2 less now than I paid. If you don't have to have a name brand, these should do the job. - Bob


"Amazon" Generator & Water Pump Belt

 

I'll just echo the "don't make them too tight" sentiment. I lost the generator bearings on one road trip to Canada and lost a waterpump on a x-country road trip. That was a major inconvenience, but I found out Sac Vintage Ford did overnight shipping to Illinois.
An inch of deflection is good.