The old MoPars work quite well on 6 volts. The only reason they changed to 12V negative ground in 1956 was to accommodate the new transistor radios. If you really need to add power steering, the one available as an option from '52 - '54 is a bolt-on. The front brakes have 2 cylinders per wheel and 2 leading shoes, so power brakes are not needed.
Engine parts are relatively easy to find because Plymouth and Dodge shared blocks (Plymouth had a 1/4 inch shorter stroke through mid '54). While there were several different gearsets and most Dodges use a long input shaft, manual transmissions are interchangeable from'39 through '56.
