OK- - - -next suggestion- - - -the current regulator (behind the "ARM" wire terminal) is in series with the voltage regulator winding. If it's set a little low, it can interrupt the field current and cause a fluctuation in charge current. Try increasing the spring tension on those points a little. It's beginning to sound like my "Use Delco parts" advice is going to apply in this situation. Too bad I can't drop by and tinker with that one- - - -it sounds like an interesting challenge! Be sure you've got a good ground between the regulator base and the generator housing. I like to run a wire between those two parts to assure there's not a high resistance ground path from the engine to the firewall. That can cause all sorts of oddball charging 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!