The only thing to change to convert the gauges to work on 12 volts is the gauge lights, and a resistor in line with the fuel gauge. I would assume the truck is now 12 volt, and someone has done this already.

Nice looking truck.
Grigg

•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-