Jeffry,
I don't know anything about a '55. But before I restored my '36 Chevy pickup I ran it as a daily driver sbc powered rat rod with 12 volt electrics for about 50K trouble free miles in the 1960s. The original '36 gas sender and gauge worked fine on 12 volts with no voltage reducer.
Now decades later the '36 is restored in every way including 6 volt electrics and the exact same sender and gauge are still working perfectly. So at least on a '36, the voltage makes no difference in the gas gauge function.
