I don’t understand why you would use shunts on the stock ampmeter if that is what you are proposing. The stock ampmeter only works correctly with the full load current going through it.
Shunts must be matched to a meter that is designed for the shunt. An ampmeter that uses a remote shunt measures the voltage drop across the shunt (it is really a voltmeter). The stock gauge has the shunt built in already, so it measures the whole current in the wire.
