Been running a 51 Plymouth on 12v for about 2 years now.

I forgot about the wipers, mine are electric and I built a current limiter to slow down the wiper motor. Poorboy is correct about the wipers working real fast on 12v. I am not sure which would happen first, smoke or the linkage getting beat to death. Obviously, anyone with vacuum wipers doesn't have to worry.

As for the starter, been running that on 12 just as well. No issues. I talked to a local starter shop about converting it to 12. According to them, that can be done, but you don;t need it as long as the engine starts easy. Mine does. If I eer burn it out I'll spring for the conversion, vintage powerwagons may still sell a 12v starter. These guys make a modern ministarter for it

https://snap-usa.com/products/1950-1955-dodge-plymouth-mini-12-volt-starter-replaces-mch6101

As for the fuel gauge, a runtz resistor (it's not really a resistor) will take care of that, the rest of the gauges are mechanical except the ammeter and it don't care about voltage. If I was just going to spin it over and see if it started I'd use a 12 battery.

To be honest I would give the wiring harness a real close look, odds are if it's original it is falling apart as we speak. If it is I wouldn't use it. I'd disconnect it and run a jumper wire or two for testing the engine.