all mopar of that vintage would be 5 volt gauges.
you don't "need" the circuit board.
it is designed to allow 1 VR to supply power to all the gauges, and centralized point for the plug for lighting and gauges etc..

you could wire the gauge independently.
you would have to supply it with 5 volts however and be sure you isolate it from ground.

there is a solid state 5 volt VR design in the tech archives. you could build that and wire directly to the single gauge and make it work.

otherwise if you must have 12 volts you are better off buying an aftermarket gauge and changing the face plate.