The next time it won't start, pull a plug wire & put a metal wire in the boot. Turn the engine over & place the wire close to something metalic ( non fuel related) under the hood. If it doesn't spark or arc, It is electrical. If it does spark, the problem is elsewhere. This will at least let you know where the problem is or isn't. I would change the points, condensor, Distributor cap & rotor. As stated before, make sure all wiring to & from the dist is secure. I don't know if it could be the coil or not, I have not heard of a coil working & then all of a sudden not working. Jon