On my 235 (54) it was the fuel pump that was causing this issue. I had the factory style (no bowl/non-vacuum assist). It would test fine and then quit later, I went with a very reasonable $20 eBay electric pump and have not had a problem since. My truck did exactly the same things you describe the new pump fixed it.

1950 Chevrolet 3/4-Ton 3600
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