Incorrect Timing Adjustment causing heat issues?

Dana67Dart said
Sounds like my 67 273 2bbl.

With vacuum advance on it misfires at around that same rpm. I'm at 5 before.

Spec is 5 after (CAP)

I checked the dwell and with the vac on it goes down way down and starts to misfire. Without the vac the dwell stays fixed and no misfire. Could be too much total advance? Could be dwell changing too much?

You dusted off an old memory with your comments above about variations in dwell.
That is the the 'point cam' wearing out and causing said issues. I've had to change several of those way back in high school .
Today's points are not what they used be either...
Also too, factory tuner is almost never optimum.