Amp gauge shunt

I have bench tested several A body Mopar ammeters and some of them were marked +/- 40 and some were unmarked. Full scale deflection on all of them was 40 amps and they were surprisingly accurate. The old ammeters depended on current flow to create a magnetic field to move the needle, the ones with a remote shunt, measure the voltage drop across the shunt (in millivolts) to move the needle. Meters are calibrated to work with a specific shunt resistance and changing shunts throws everything out of calibration.
I agree with Crackedback, I don't like ammeters, so I disconnect them and install a small digital voltmeter in the ashtray. Just close the ashtray and everything looks totally stock.
As far as bulkhead terminals go, if you look at the data sheets for any 1/4 inch spade connectors, you'll see they are all rated for a max 40 amps. Why in the world did Mopar design an electrical system limited to 40 amps and then install 60 amp alternators.
I personally connect the alternator to a power stud going direct to the battery and use a Bussman power fuse module direct off the battery with relays powering lights, fans, and anything else I can to keep as much power out of the car as possible. The less power you run through the bulkhead connector, the more your car will love you for it.