[jhv48]

What you describe could be a few things actually.

Could be vapor lock, plugged gas tank vent or fuel line or a failing coil, among other things. I like the idea of bolting on a buddies carb and then testing. That would eliminate the carb from the equation.

Then I would start with the coil. Not sure how you would do that without replacing the entire distributor. They usually show signs of failure when good and hot. Replace with a friends and see what happens. Next would be vapor lock, or fuel lines partially plugged. Fuel lines running too close to headers or other heat source. Carb could have fuel boiling in the float bowls. When the car is hot, pull off the air cleaner and listen and watch for fuel boiling out of the bowls.

Got to be something simple. Heat is the catalyst.