1958 Ford 861 Tractor

I wired my 48 willys from scratch.
I am using 12v.
What needed to be done is wire in a mopar 2-pole ballast resistor and use a 12v external resistance required coil.
You will need from the start switch to provide 12v to the coil only when cranking.

If you wire it the same as any 72 and down mopar you should be golden.
6v starters last a long time when running 12v thru them, just do not crank on them long periods of time or get them hot.

Are you still running a 6v generator? If so convert it over to a gm one wire 12v.

Also 6v wiring is heaver than what is needed for 12v so as long as it in good shape you should have no issues.