not disagreeing with anything that's been said here but it sounds an awful lot like Vapor lock or boiling fuel in the carb. We have been seeing more and more of this in the shop especially if one is using ethanol based fuels.

If you haven't already checked, when it dies immediately check the spark. it fit's strong and steady I'd go back to the fuel.
We just had a 65 olds this week that has been dealing the owner fits for 6 years. he even put an electric pump on it to try and get around the vapor lock issues. Root cause was found to be a clutch return spring limiting the heat riser butterfly opening. This in turn prevented WOT operation and also would overheat the intake thereby boiling the gas in the lines and carb. Moved the clutch retrain spring and it now runs like it should and hasn't in over 6 years