You need a new starter drive (the part with the gear), not the whole starter. Most of the online vendors and local parts stores like NAPA should have the right one in stock. The 56 should have the 12 volt starter with an armature shaft about 1/2" I'm diameter.
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
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