Frankendart Lives!
Well, looks like the issue resides in the carb tuning. I leaned it out some, but it still shows rich when cruising. Figured I'd unplug the MAP sensor to negate the vacuum advance curve as a test and the thing doesn't skip a beat when you hammer down now. It's running rich enough that it doesn't need the advance on cruising, so unless I buy some more carb tuning pieces I guess I'll just leave the sensor unplugged.