1956 was the first year Mopars used 12 volt negative ground. (At least for USA and for cars.)
My 49 Wayfarer had six volt positive ground. I converted to 12 volt so it could run the same battery as the rest of my cars. And also because most six volt over-the-counter batteries you get at your local parts store suck.
My wipers are vacuum, I don't have a heater or working radio, I used something I forget the name of on the headlight switch, replaced all the lights and bulbs with 12 volt, switched ammeter wires, 12 volt GM one wire alternator, and a lightweight 12 volt starter from Hot Heads for a Dodge hemi V8 (had to re-clock it), Pertronix electronic ignition and 12v coil. I think that's all.
The six volt starter worked with 12 volts, spun real fast, but if you had to crank it for more than a few seconds, it crapped out.
Early Fords and Chevies also ran 6 volt positive ground until the mid-50s. I think they went to 12 volt negative ground in 55, but don't quote me on that.