I have been reading through what all you have done. The problem from the beginning sounds like a bad coil to me. Back when your vehicle was young, it was quite common In fact a spare coil was one of the spare things we carried under the seat our GMC's back during the 50's. When coils get hot, they expand. If the insulation is bad, the windings can ground against the inside of the can. The problem isn't very common today because I suppose the insulation is better. If you have a coil around that is known to be good, try it. If you don't have a coil around, I would suggest buying a new one. I think it's worth a try with all the trouble you have had.
