Aight Bewy.......

Dr.C.
For the GM adj units, I have the chart for an Accel unit.
The points type starts to pull at about 4.5", HEI at about 6". The chart is really confusing because it shows the vac starting from the max of 9 turns [ points dist ] 7 turns [ HEI dist ] starting from CCW [ the stiffest spring position ].


As the plunger starts to pull in, even at low vac, the vac is going to increase slightly, & help pull in the plunger even further. This is going to vary with each combo.

RRR.
The VA made no difference? Did you check the timing with VA connected to see if the VA actually added any timing? To tell if VA is going to add anything, better to do the rpm test in post #5.

To all.
Both the Accel & Crane adj vac units have a sleeve inside the spring that limits spring travel. A most stupid idea because you can get a situation that the VA locks up, just goes solid. I prise these units apart & remove the sleeve. I use a lot of Chinese HEI dists here, never had a problem; they come with adj VA & do NOT have the sleeve. I can buy a Chebby HEI here for $80 that has the good VA unit, Crane adj VA unit would be about the same price!!