47 chev,
The 6 volt gauge and sending unit are calibrated to operate together. The sending unit is a variable path to ground that changes with fuel level and influences where the needle sits. This combination of electrical values needs to stay constant for the system to read correctly.
The only easy way to accomplish this is to reduce the voltage to the fuel gauge with a small voltage reducer (resistor!). This provides the gauge and sender with a voltage that won't burn them up and one that makes the gauge read properly at any fuel level.
I think you have already figured this out!
Stuart
