Rather than guessing at the coolant temp, get a mechanical gauge on it. They're cheap, then you'll KNOW what the temp is. Somewhere between M and L means nothing.

The 460 makes it easy, as there are two water jacket ports in the intake manifold.

 

Exactly even if you just have one that you use for diagnosis. I actually have a mech temp gauge and a mech oil pressure gauge I use for diagnosis purposes and install temporarily in a home made case with magnetic base that can temporarily be mounted to the cowl/hood. A mech temp gauge is way cheaper than a new rad.I do suspect that your rad may be the culprit and is not quite up to snuff.

Best part is a mech temp gauge can quickly be cheeked for accuracy by dropping the sensing bulb in a pot of boiling water.

You may not need to replace the rad it but may just need it cleaned out. Any old school rad shop should be able to dip it in the hot tank clean it out, pressure test it afterwards, and do any repairs for any leaks that pop up.

That is providing local laws have not made hot tanks illegal.

 

I had a similar problem.

I put my fuel filter on the frame at the bottom to keep the gasoline in it cooler. I ran my fuel line across the front of the motor to keep it cooler. I put in a fuel pressure regulator and gauge. Put in a Eldebrock fuel pump with the Elderbrock carb and run it about 4 lbs. Insulated the gasoline line and kept it off the hot manifold. Rebuilt the carb and something there fixed the problem.

 

I will look into installing a mechanical gauge in the near future to assist in troubleshooting this issue. Also, roughly 8 months ago I had the radiator gone over at shop because it had developed a small leak on the top of the tank. I was told everything checked out and that it was in surprisingly good condition considering it's age.

Now, today just for fun I pulled a super cooling radiator out of a parts truck I had and swapped it into my truck along with the correct fan shroud. I drove around some, but never let it sit and idle long. Going by the dash gauge it was a touch cooler perhaps, but without my temp gun all we can do is guess on that matter.
Anyway, I parked it, let it idle in gear and it died again after a few minutes much like it did when I was waiting for the train earlier. It also restarted immediately never running rough or anything else unlike the previous incidents where it wouldn't start for a little while.
It did it one more time while I was turning it around to park it for the night.
This time I was on the gas a little and it died like I lost fire, but once again it started right back up and ran fine. It almost feels electrical now, very different from the previous events, but still under similar circumstances.

 

That doesn't sound at all like vapor lock any more. Sounds more like an Ignition Control Module. Only dies on you when the airflow over it stops. Yet starts right back up.

It will probably continue to do that until one day when it just doesn't restart.

 

I am starting to suspect that now. I'll swap a known good spare on in the morning and see what happens. I would suspect the pickup coil in the distributor as I did change that shortly after swapping the engine, but I would think it would take much longer to cool enough to run and be less affected by airflow given its location. Replacing and insulating all of these fuel system components did seem to change things a little, I wonder if I had a little of both going on....

 

A very real possibility nothing can drive a person more nuts than have two different things crater at near the same time that exhibit similar symptoms.

 

I swapped the duraspark out today for a known good spare, drove it around town with no issue, but didn't sit long either. Once I got home I let it idle in gear for a bit and it died once more after around 8 minutes. I got it to do it a few more times but it always restarted right away, although twice it stalled right after restarting but would start up right away after that.

I watched the fuel filter by the carb this time, it wasn't always full but fuel was pumping into it as the engine consumed it. Nothing looked out of whack there, but eventually it stalled, fuel still flowing normally.

I suppose it could be the pickup coil in the distributor, or the ignition coil itself... I would think the pickup coil being where it is would be less affected by air movement and give me trouble in conditions other than idle with the ac on.

 

What are the typical symptoms of the ignition control module malfunctioning and pickup coil malfunction?

 

I tried a new pickup coil today, and it didn't solve the problem either. So, that left only one thing, the ignition coil. While the truck was idling I gave the coil a whack with my hand just to see what happened and the engine died.
I started it up again, gave the coil another whack and the engine died again, only this time it would not restart. I replaced the coil with an accel super stock with the hope that since it costs a bit more maybe the quality control standards would be a bit higher than the house brand at parts store (probably not).

I've since driven the truck around some and then let it idle in gear with the ac on for more than 20 minutes without it stalling. I would have never guessed the ignition coil failing would cause these symptoms... I'm used to them either working or not. It does make me wonder how long it had been on the verge of failure seeing as it only quit under specific circumstances.

Hopefully this is the end of it...

Thanks for the help and the suggestions

 

Congratulations on finding the apparent problem.

Make sure the voltage is correct. The factory coil likes 9v. Most aftermarket coils like 12v

 

I thought about that, but it seems to run just fine, possibly better than before so I think I'll leave it be and see what happens. I would think it would potentially last longer and not get so hot running at reduced voltage.

 

My 79 400 did exactly that. Tried all of the usual...turned out to be the rubber fuel lines from the two tanks was so old it collapsed under vacuum and finally stalled the engine. Switching tanks used to fix it for a while, but then it happened with either tank. The only way I could get it to start before a full cool down was to disconnect the fuel line at the carb and crank the engine until fuel started to flow, but it would only stay working for a few minutes, then stall again. Usually happened when I stopped after a heavy load. Died at idle and wouldn't restart.