[BillyJack]

Subscribed for your final evaluation.
In the 70's, I would always move my vac advance to a manifold vacuum port. It really only affects the amount of advance at idle, since the ported advance comes in just off idle. Some of the 80's non-computer truck carbs wouldn't idle down low enough, so I had to move from manifold to ported vacuum. I always felt that manifold vacuum gave a bit crisper response off idle, but it certainly wasn't a huge difference. I'll be curious to hear your thoughts after trying it both ways.
BTW, 34-36 degrees @ 2500 rpm sounds like a real good place to start for your total timing. IIRC, 2500 rpm was what you got with the middle springs in the old Mr. Gasket 3 spring kits. As long as you used decent gas, it worked well on a bunch of near stock street SBCs I tuned over the years.

Bill

 

[BillyJack]

As far as I know, adjustable vac advance cans can only vary the limit of advance, not the rate. We're going back a long ways so memory is foggy, but GM at one time offered different part numbers with different degrees of advance. Hi-performance cars, such as Z28s or Corvettes with higher initial advance settings (10-12 degrees vs the normal 4-6) got smaller vacuum advance ranges. Before adjustable cans, we'd fabricate stops in the slot to limit the advance at high vacuum conditions.

Bill