On cars I have worked on with problems similar to yours, the fuel problems went away when we installed a Mallory 4309. We install the bypassing regulator after the carb. This keeps the carb and the fuel in the carb much cooler. Also if you have a fuel log or worse a fuel filter bolted to the engine (like the original 427 cars) you will have vapor lock problems.
http://www.jegs.com/i/Mallory/650/4309/10002/-1