OP - thanks for the added information.
Something else to consider, and I don't know on this vehicle.
On some mid to late 1960's Pontiacs, it is a well-known fact that one can get a stumble at the end of first gear under hard acceleration IF the fuel tank is less than half full. The pickup is in the front of the tank, and centrifugal force throws the fuel to the rear uncovering the pickup. No pump will pump fuel if the pickup is in air.
But listen to Jerry on the Holley. Other makes of carbs are more my forte.
Jon.
