Did you happen to look under the distributor cap for worn insulation on any internal wiring? Since the breaker plate doesn't move on a stovebolt distributor, it's not a common problem, but a pinched or mis-routed condenser wire can get grounded out intermittently and cause problems. The insulator that goes through the distributor housing can also be a source of random ignition problems.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!