Robert.
I got a day without rain!
I drove it with vacuum advance disconnected and it still popped/backfired.
I will report what I noted, but its not very technical.
The pop only when I nailed it rapidly after about 10 min of diving. It happenedd on a level or slightly downhill grade and the engine was around 4000-4500 rpm(, by the time I looked down it was falling through 3500 rpm.
This is NOT the way I intend to treat this car on a daily basis, but I will have to get up therein RPMs to pass occasionally

so it seems as if the vacuum advance is not the culprit, but I'm not sure.
Whats my next move?
thanks
Vic