VAPOR LOCK and related fuel boiling issues seems to be the "thing" nowadays. I had trouble on my own car. Here's some of the things I did, and some of it takes work
First I'm a huge believer in vapor return systems. First one I ever saw was on my old 70 sixpack RR "back then" and it WORKS.
You can add one easier / harder, depending on what you drive. Older cars you will have to add a third tube back to the tank, and figure a way to GET the tube INTO the tank. On my 67, I silver brazed a tube right into the face of the tank, above the rear axle, after draining the fuel, and filling the tank with CO2 from my MIG.
Wix makes the "front part" easy, as they and others make metal fuel filters with a built in return port (used on some AMC products in the 70's/ 80's) part not 33040 for 5/16 line, and 33041 for 3/8 line.
These have a 1/4" return port. You can hang the filter can either vertically or horizontally, so long as the 1/4" port is "up." This port returns a small amount of fuel through a built--in orifice to the tank, which does TWO things
One, it constantly returns some fuel, keeping vapor bubbles to a minimum, and when you shut off the car, it immediately releases pressure from the pump to the carb, preventing fuel from "pushing" up into the carb from pressure
Another thing that helps is to change to an electric pump, mounted at the tank. On my car, I just ran it through the mechanical pump, but I eventually plan to remove the mechanical pump.
And, you can buy thick spacers under your carb to isolate the carb from too much heat build--up. If you live in a warmer area, or mostly drive your car in warm weather, you can remove the intake manifold and plug the head crossover that runs under the plenum.
Of course you want to make sure the carb is set-up right. "pouring gas" out the sight plugs SOUNDS like the floats are set too high. This may take some "dirty fingers." I'd adjust them down some, and try to check the float before the engine gets very warm. This will show you whether it's from pressure build on hot shutdown, or whether the level is just plain too high.
You can get SOME idea also, by just holding the throttle at a "simulated medium cruise" RPM and looking down the throats. If you HEAR a sound like bacon frying, as droplets of fuel are sucked down, or SEE droplets out of the venturi boosters, the level is creeeping up too high.
Generally, mechanical pumps HURT you for vapor lock/ fuel boiling, because they must 'suck' fuel, and cause a low--pressure area in the fuel line, which tends to boil when going past hot exhaust/ other areas.
Yet another thing to check is that your tank IS getting vented. On the early cars, the vent is a fitting high up on the filler tube, inside the trunk. This tube then comes down the side of the filler tube, pokes through the gasket/ seal on the trunk floor, and ENDS inside the frame rail. I spose it's possible this could become rusted shut/ other problems, but worth checking.
I found one in a junk yard that had been PLUGGED by a human up inside the trunk.
