Should not have had a 6V battery. The owner must have just installed the 1959 motor and didn't finish the "conversion"/install....or slapped a battery in there to look good for the sale....or did not know what he was doing.

You can tell by the pinion shaft/armature shaft diameter if you still have the starter. 1/2" for 12V, 5/8" for 6V. Probably was a 12V. you are good to go.

Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn