Ammeter to Voltmeter...who does it?
I ground this part off mine with a rotary file in a high speed straight air grinder to allow the gage needle to swing. Your conversion looks pretty square in there i wouldent move it. If you move it up any further your volt gage internals wont be hidden but will be easily seen. Of course to grind out the spot in your housing for the gage needle to freely swing, you have to remove all the gages from the housing because of metal chips when you grind out the center pin.
I insulated the red feed wire with a plastic grommet going thru the housing, and 2 thin phenolic washers. One on either side of the metal gage housing, but i used metal washers to ground the negative gage stud to the metal housing this way you only have to run one feed wire. You can run that 12v volt gage positive wire right over to the 12v input feed that sends gage cluster power into the voltage regulator in the fuel gage. Remove the stamped nut that holds the fuel gage in the housing that is also the 12v feedcoming in, use a washer, a nut and a ring terminal and tap in.
I also clipped the old needle off the old ammeter, and clipped the needle of the new volt gage short to glue the ammeter needle to it to complete the mod. I also hooked the newly modded volt gage up to a car battery charged to 13.5 volts, checked with an volt ohmmeter, and while the gsge had power running to it , i adjusted the needle where i wanted it to point to by adjusting the potentiometer on the volt gage internals to tune in the pointer