If your stock motors work, why not put a resistor in the circuits for both motors for the 12 volt conversion. That is what I did on my '42 and they work great. I don't remember what resistor was used but someone can chime in with the answer, if that is the direction you would want to go.
Kent
P.S. This would work from Jim Carter http://www.oldchevytrucks.com/cart/product.asp?prodid=EL135&i=9776||||| Use one for each motor.
Last edited by Lightholder's Dad; 12/12/2018 5:12 PM.