I'm trying to build a voltage regulator for my fuel gauge,but not what the voltage should be to the gauge.so if anybody could tell me the specs and the parts I would need for it,I would be grateful. The gauge is on a 72 gmc pickup c1500.

What is it your trying to accomplish with the gauge?

Aren't you really asking about a fuel level sender that will regulate the signal being sent to your gauge?
If so, they are available in the after-market that can be adjusted and installed to do just that. So long as the fuel level system has the correct harness, along with a sender circuit, you should be able to adapt most to your application.
Remember, the fuel level sender is basically a variable resistor calibrated to the gauge.