You will need 12 volts for the compressor clutch, and also the blower motor. There is a chance you can get some sort of electrical thingy to convert from 6 to 12, I think they make them to run newer radios, but not sure if they are powerful enough for AC.

I have not installed or bought the system for my 48, but the research I have done leads me toward the Classic Auto Air Street Rod Cooler II unit. I think, after a phone conversation with them, that it is better unit than the one they sell as a "perfect fit" kit for my truck.
I think I can do a neater job of installing the street rod unit than the other one in the kit.

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-