Dave,
Like Tiny I ran my 1936 Chevy pickup with the original 6 volt gas gauge and sender for about 5 years and 50K miles as a 12 volt daily driver "rat rod" (V8 engine, B & M "Hydrostick" transmission, etc) in the 1960s with no problems. Now that same '36 is restored to original, including 6 volt electrics, and the same gauge and sender are still working fine back on 6 volts.
So the "converted" gauge seems to be a solution looking for a problem.
