Timing by Vacuum Reading?

First mistake. Not having vac adv on a big cammed engine like this. The VA unit needs to be adjustable to work with the lower-ed vac of the big cam.

Second mistake. Using a vac gauge to set idle timing & mixture. Might work ok with stock cam, but useless with large cam & gauge needle bouncing around.

Third mistake. Choice of buddies.

Fourth mistake. Buying a useless big bucks MSD dist that [a] has no vac adv & has a magnetic pick up that has less cyl-to-cyl accuracy than a stock Mopar dist.

This is the first thing you need to do, then report back with the result. Five min test:
[1] warm up engine, put into gear if auto.
[2] Engine idling, loosen dist clamp
[3] Slowly turn the dist CCW, starting from about 12* BTDC. Idle rpm will increase & get smoother [ how do I know this? ]
[4] Keep going CCW until you reach the highest idle rpm.
[5] Then toggle dist CW/CCW until you are sure of highest idle rpm.
[6] NOW check the timing. Do not be surprised if it is 30+ degrees. That is a guess on my part because you haven't provided the cam specs.