vapor lock???????

WHEW! I just read something on this that happened to older Ply's and Dodges in the 40's. What they did to fix the problem was to install a heat sheild around the fuel pump. Also, keeping the fuel line as far away from anything period will help.
Check to see if the carb is boiling fuel. You might have to investigate how to cool the carb down some more if such is the case and why it is getting so hot.
The rest of the system (Cooling) should at least be looked at. Good coolent, good rad flow, etc......