[Jack21]

Probably a silly question, but should you be using a vacuum advance distributor, it stacks up this way. 12 - 14 deg initial, plus 18 - 22 deg mechanical (all in by 2200 - 2600 RPM), plus 20 deg vacuum and you have 52 - 54 deg total adv at high vacuum. Engine will miss. Disconnect vacuum advance. If missing stops, that may be your problem.