[Mike Taylor 3601]

The way you say your timing is jumping around,it sounds like ignition control/box problem.
I have used alot of pertronix on restoration projects have'nt had any problems,I use ignitor 3 has protection circuit and built in adjustable rev limiter,pertronix tech line has always been helpful when I have called,oddball installations, I would probaly give them a call.
I keep a hei w/wires so I can test and elimnate whole ign. system@ one time then have hei setup for msd so can determine box or dist.
Don't take for granted that any part can't be or go bad.
Mike Taylor 3601