If the headlights get dim while the misfire is going on, you probably have a loose wire coming off of the ammeter.
That happened to me once. Some dill weed mechanic didn't tighten the nut on the ammeter. I would have fired him on the spot, but since I am a one man operation, I had no one to fire...

1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission