I had a similar symptom with a 47 Mercury with a flathead V-8 back in the early 1960's. After all the diagnostic tests I've described, including changing to a Carter fuel pump, it still had 14" of vacuum on the fuel line where it entered the tank. The problem turned out to be a 2" long grasshopper in the pickup tube in the bottom of the tank. The car would run about a mile, stall, and refuse to start for 10 minutes or so while enough gas leaked past the restriction to refill the fuel line.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
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