I would bet on high resistance plug wires. One can also check for high voltage leakage by looking the the running engine in total darkness. That's particularly effective if it damp out.
1951 3800 1-ton "Earning its keep from the get-go" In the DITY Gallery 1962 261 (w/cam, Fenton headers, 2 carbs, MSD ign.), SM420 & Brown-Lipe 6231A 3spd aux. trans, stock axles & brakes. Owned since 1971.
