vacuum gauge to solve idle issue

So now the surging issue has been solved with distributor swap.
I wanted to fine tune the timing. I decided to leave factory 4bl Carter carb and the distributor from 84 360 1/2 ton in the cuda.
I have vac gauge, Mighty Vac, old school timing light and tach.
Verified tdc.
Initial 20* (vac can plugged, gauge hooked to ported vac on carb)
3.8" hg
575 rpm idle in gear
37* all in @ 3300 rpm
18" hg @ 3300 rpm
Approx 55-57* with vac hooked up.
Vac can has 7r stamped on the arm.
Suggestions/advice/improvements?
I seem to be able to advance to the point of 30* initial? (no pinging) Why so high?

Thanks all