If you want an original looking harness I can also recommend YNZ. I bought the harness for my '38 from them. The cloth covered harnesses are expensive. Why convert to 12v? If you're just wanting to push a radio you can buy a step-up to power it unless you want a door thumper.

Save a life, adopt a senior shelter pet.
The three main causes of blindness: Cataracts, Politics, Religion.
Name your dog Naked so you can walk Naked in the park.