If the vacuum advance is in the way of the distributor hold-down bolt, there are two simple solutions: (1) buy the correct offset distributor tool from KD or (2) rotate the distributor 180 degrees and insert the wires in the correct holes.
I have been road-racing since 1960, and the small block Chrysler in an A-body works quite well. There are two brothers racing an A-body Cuda and Dart with the 4-speed and 273" in the Philly area in SCCA competition. There was an automatic Cuda permitted in the original Trans Am racing forty...