Check the centrifugal advance for free movement. That one's easy- - - - -it's right under the distributor rotor- - - - -no distributor disassembly required to inspect/lube the weights and springs. 50 years ago those distributors were notorious for the weight pivots to get worn or rusty, and since there's no oil in that part of the distributor, the weights and springs were SUPPOSED to get a dab of high temperature grease (same stuff that's used on the point rubbing block) at every tuneup. It virtually never happened, so the weights are usually rusty and ratchety. A momentary hangup of the advance weights will create a stutter or stumble.
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!