Ok, I must now say that everything that I thought I knew about vacuum advance is now out the window, and I admit that I don't know jack...
So today, I installed the light springs into the Pertronix to advance the mech advance curve to kick in starting at 1k and all in by 2400-ish. Reset the initial timing to 11* with vac adv disconnected and idle at 500rpm, and 38* total timing at 2500+. I also tried adjusting the carb with the vac gauge, adjusting richer on each bank by 1/4 turn until vac peaked and just started to decrease then backed off 1/2 turn. I decided to try swapping over to the timed vac and see how things worked out, and this is where it started to get wonky.
Plugged in timed vac, and timing was still 11*. Hit throttle and watched vac and timing. At 4000rpm, I had 55* on the gun, which is the 11 static + 26 mechanical + 18 presumably from vac advance. Ported vac was still at 17" at 4000rpm so ok course was all in... I always thought that the vacuum signal would be down close to zero as rpm went up, but that does not seem to be the case. I tried swapping over to manifold vac on carb, and the only change was idle rpm went up to 700.
i have not had a chance yet to drive it to see if it is still bogging... Will try here in a bit and will report back.
vacuum advance theory vs real world is making my head hurt...
thanks all!
Update: so took it for a drive. Overall, drive ability is good, everywhere but from low rpm and hard acceleration. From a stop-to-WOT, motor bogs down and kinda chugs for about 2-4 seconds then finally starts to accelerate. No backfires, no pinging. Hard Acceleration from cruise speed kicks down transmission and does not bog. I had no pinging/detonation. It ran quite well but for the low end acceleration... Maybe my desire to burn some rubber every now and then won't be fulfilled... Funny thing was I could get a decent little squeal with the original 2bbl setup...