Quote:

6.5 PV in it but last time I checked vacuum at idle it was under 7.





This looks like a problem to me Do you have a 4.5 laying around to try?

Usually popping back through the carb is attributed to early ignition timing. I'd start from square one and put on TDC, confirm distributor shaft is in the proper location, then do as MR PBody said to set up your base timing.