That's good info at the FORD website.

My neighbor who is a retired Buick mechanic told me he upgraded to 12v an old '50 Chev he had. With a 12v generator in place, he just bought one more 6v battery & wired it in in series. Now it's possible to tap off either 6v battery to run things like the original radio and anything else you dont want to go out & buy 12v parts for. The starter he left 6v but fires it up with 12v. As long as you don't hold the starter button down for extended periods it works just fine and spins much faster. You would have to replace the 6v starter with a 12v one anyway so get all the mileage possible out of the old one. He said it lasted untill he sold it a few years later.

Ado