""The timing is set at 12* initial, and the idle is set at 1100 in park/neutral, but it drops down to about 550 in gear. Vacuum in park is about 16-17, and in gear drops down to about 11-12""

Since your timing at 1100 N is 12 degrees is the same as the timing in gear, then this might be a carb idle circuit problem which might indicate that the carb is lean in D. (I wonder if your springs are fluttering in D which would make it rich?) Try tuning the carb once you have the motor up to running temp and since it is an auto, then tune the car with the tranny in D and the emergency brake applied. Then you can readjust the carb for the highest vacuum while in D at the desired rpm. Tuning an auto car for best vacuum while in N is fine to get you close, but an auto street driven car needs to have the final tuning done while in D with the brake applied to simulate actual driving conditions.
Note: I have had 6 carbs on my 340 and the worse performing carb by far was the Edy Performer 750. The Edy Performer 600 was a much better idler/performer carb.