Drop the dust cover off the bottom of the bell housing and mark one ring gear tooth with chalk or paint- - - - -then bar the engine over and count the teeth. 139 for 6 volt engines, 168 for 12V. The original engine would have been a 6V system.
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!