1973 Holley 1920 Accelerator Pump Question - Stumble Off Idle

This may not be your answer to your problem but here is what I found on a slant with a stumble as you are describng. The timing chain was the issue. Take the distributor cap off. Rotate the engine back and forth and see if the timing chain has slack and how much by watching how much movement the crankshaft has before the distributor rotor moves. This could be your problem if it does. I have seen this before. Just something that is an easy check to cross off.