Both starters have a 9 tooth gear- - - -the difference is in the diameter of the pinion gear and the diameter of the armature shaft. The 6V shaft is noticeably larger than the 12V, so the starter drives do not interchange.
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!