Tuning an Edelbrock 650AVS on a stock 340

Mean.
Considering the combo, 25* at idle, as you have discovered is ideal, & about what I would expect with years of experience doing this.....

Idle rpm varying. Make sure the VA plate inside the dist moves freely. Is it an adj VA unit? Also make sure the centri weights move freely. The VA can have 25-30* of advance. How did you get 25* for idle? Combination of init +MVA?
How much idle vac now with 25* at idle?