I need some help with an old Dodge truck.

j par said
If 12 volts were absolutely necessary somewhere it would seem like a 12 volt alternator could be tethered in as well as a 12 volt battery to run whatever needs 12 volts? A stereo?...

The truck needs a full rewire so why not?

With a 12V system the owner can buy parts easy and off the shelf.

The biggest reason is the engine cranks so slow on 6V.