I had the same problem but not as serious as yours. I run a edelbrock 800 carb. I put a carter electric (the low pressure one that don't need a regulator) pump back at the gas tank and isolated it real well so I can't hear it. Completely solved the problem for the most part. Primes the carb before startup when the engine is hot. No more long cranking times.

I was running out of gas on a fuel throttle blast when the car was hot. Bypassed the mechanical pump and solved the problem. I'm thinking that the Mechanical pump actually heated up the fuel and made it more prone to vapor locking.

I did have a filter just before the mechanical pump so that may have exsaperated the problem also.