I gots a problem!!! Please help!

The 340 in my 71 Van got to doing the same thing so I easter egged in a coil I had laying around. Low and behold it ran, but only for a while. Swapped in another used coil, same thing, ran for a couple of months and quit. Did not seem to matter whether I was running the points setup or Mopar electronic ignition, because it happened with both. Odd two used coils would out and out quit. I thought it might be too high a voltage (bad regulator), but never got around to checking it.
Not trying to highjack this thread, but one of my buddies has been successfully running the setup for years on a slant motor, so I've decided when the 340 finally goes into the Duster, I'll be running the Mopar electronic distributor with a GM four pin HEI module, and a Ford 5.0 junkyard coil I bought when I had a stumble/no start problem on the blue fox body convertible and it turned out I just needed to notch out a TPS mounting hole to adjust the output voltage.
Another no start problem the van had at one time turned out to be from the main 10 gage wire supplying electricity to the interior through the bulkhead connector. Corrosion had caused a bad connection and the resulting heat toasted the connector along with the spade connectors inside it. Hogging out the hole in both sides of the bulkhead connector and replacing the burned male/female spade connectors, along with a length of the 10 gage wire near the connector with overheated funky insulation fixed that problem.
A better solution might be to run a 69 GM style charging circuit and keep the high amperage out from under the dash entirely.