Ampmeter into Voltmeter?

I've got a 66 Barracuda and don't really want to change any of the gauges. I've seen a lot of threads about removing the Ampmeter, no problem there. Couldn't you just hook "voltmeter" wires to the gauge? I know it will show movement to the positive when power is applied. I think you could cailbrate it way putting different voltages to it and marking the gauge with very small lines on both sides of zero. (so it looks the same on both sides)