64 Plymouth 273 Intermitent severe misfire.

I've always heard that a condensor is always suspect. Change it and the points and set them perfectly of course. Next I always drop my fuel tank and clean it out. Yeah, it totally sucks but it's a good feeling to cross that off your list. You could be sucking up some tank debris every 10 minutes or so and clogging the pickup tube, which means zero fuel pressure.

I'd also test an extra carb.....some old original carbs on your engine may have been rebuilt but are "done" and junk.

If things persist after this, I'd probably run a voltmeter on your front seat on the "+" side of the coil just to affirm that your primary voltage is consistent.