Amp gauge vs volts gauge?

Hey folks.

I'm restoring a 1946 Dodge W series truck. It's on the home stretch and I'm getting ready to wire up the dash. The owner is adamant about keeping it as original as possible.
My question is this.

Can I just hook up the old Amp gage to power or is there some way to make this old Amp gage function as a voltage gage?

I have converted they electrical system to 12v negative ground with an alternator instead of the original 6V generator system.

Any ideas or input will be greatly appreciated.

Thank you for all your time and advice over the years.

Amp gauge is the 3 posts on the left in the back side pic.

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20230130_121245.jpg


EDIT- I'm not sure how I posted this in the sticky section. If a mod can move it that would be great.