On one of my Datsuns, the ballast resistor used to glow red hot sometimes when you left the ignition in the ON position. This can happen sometimes when the engine stops with the points in the distrubutor sitting in a closed position. You dont get that if you have electronic ignition (depending on what type it is, but most of them dont do it)

Why don't you get a points conversion kit such as Pertronix? Added with a Bosch HEC715 coil (ebay, AUS$65 delivered), that will get rid of your ballast resistor, condensor(s), and the dwell will be perfect all the time, no more playing with points.