I appreciate the feedback guys. Normal for me was 70s cars that are only 40 something now. I reviewed my '60s Motor manual but it didn't have much to say about it, although it does list timing specs for a lot of interesting mopars and just say to cap the vac line to stabilize the idle during the test and set to between 12.5 btdc and 5 atd depending on the model.
It wasn't recently that I tried MVA. I seem to recall starting issues as well with the initial was still set to 10 btdc and the vac advance was advancing during cranking and moving around if I open the throttle during cranking for a pump shot, so maybe that explains some models being set to atdc initial timing.
I'm going to try Woody's method when I get a chance. I've also had some intermittent problems with the HEI 4 pin conversion so that could be related. Pickups I've tried are around 300 ohms and min spec I found for the hei is 400 ohms (module has a current limiter so I am considering tyring a small value resistor in series with the pickup). Need to sort that out first. Vehicle was lean burn to begin with.