I was having a hard time getting a decent idle and among the suggestions, was to switch to a vacuum advance distributor. When I made the switch, I also changed the intake manifold so the big improvement that resulted could have been as much the intake manifold as the dizzy.

If you decide to switch, be careful not to get a vacuum retard distributor. I had two of them come my way before I finally got hold af a vacuum advance type and that came from someone in Europe where they are more common.
The difference is in the placement of the vacuum chamber. If you were looking at the distributor from the left fender (driver's side), the vacuum advance chamber is in the upper right quardant (1:00 - 2:00 o'clock) position.
The vacuum retard distributor's vacuum chamber is on the lower right quadrant (4:00 - 5:00 o'clock position)

Dennis