Hey Zedevan, What year is your car?
The Amps gauge is from a 240z and the volts gauge it typically in a 260z.
Maybe the 73 240z changed over to the Volts gauge, as the 73 240z has alot of similar bits to the 260z, that earlier 240z didnt have.
If you have a 260z then you might not have the right wiring to use the amp gauge, or you might have to do some mods to get it working.
Using dual colour leds and switching is a good idea.
The gauges have a green globe cover inside the guage, which gives the gauges the green colour, you will have to remove them if you want white leds. And you'll need to use the really bright ones, but you probably know that.
Heres the inside of the temp/oil gauge, showing the cover.