I put a 6V Timken axle out of a GMC 450 into a later '57 GMC 350, 12V Eaton-axle truck one time. Thought it would just shift faster but no, it was too fast. Had to buy a new motor. I wanted to save the owner some money by using the motor out of the original axle but the Eaton motors are different. As I recall, it was expensive. So At least the Timken motors came in 6 and 12 V. So, obviously the electric Eaton axles were made for both 6V and 12V trucks.
