aftermarket fuel gauge

If your sending unit is OEM, you can use an aftermarket gauge made for mopars. I used an "Equus" 2inch fuel gauge for a mopar, in my 66 B-Cuda, using the factory sending wire ( color coded blue), in the drivers side kick panel. I cut the wire, and connected onto the end of it going back to the tank, there. You cannot leave your original gauge hooked up, only one will work.
Disconnecting your fuel gauge might affect your other gauges. I have no factory gauges in my 66, so I can't say as to that. You also have to wire it (the gauge) correctly. Blue to sender, a keyed 12volt power source, a switched light source, and a good ground wire.
Got all my gauges from Summit. Just make sure you get the gauge with the right Ohms, for a Mopar sending unit. I can't remember the gauge #, and my car is in storage for winter. I think it was the 7000 series gauges. Equus is part of Auto Meter Gauges.
Hope that helps
Dave