64 Plymouth 273 Intermitent severe misfire.

full 12V to coil only shortens the life of the points, the condensor (capacitor) does the same, it extends point life. If that what works, your not gonna kill it by running it that way. change the ballast resistor again. Or check the coil voltage when its starting to chug. Then test across the HOT resistor with a multimeter and see what it reads for fun. It should read a pretty high resistance (low OHM). If you give the coil full 12V and it runs nice, you got no motor issues.