A Prestolite ignition without a vacuum advance is like towing a parachute behind your Wagoneer. When I replaced the Prestolite with an HEI on my 76 360, the vapor lock, stalling, and hard starting disappeared. I was always blaming my carb, fuel pump, fuel filter, gas tank, and gas lines. Still get only 10 MPG, but it was worth it.
76 Chief, T18, 3.54, HEI, Carter AFB.