I went through something like that with my 71 FJ40. It has an internal resistor in the coil. When I first got it running it would burn up the points within about 15 minutes (rough running, then backfiring, loss of power, then a sudden eerie silence). I was told to use a GM external resistor for trouble shooting, and that worked fine as a temporary measure. I think any ballast that drops the voltage to around 8-10 volts across the points will do. Don't try running long without any resistor or you will burn your points, and they are rather annoying to change.