Amp gauge shunt

To be honest I am not a automotive electrical engineer, just knowable enough to be dangerous. What Dodge in the late '70's to '80's with pickups with the 100amp alternators was to use the same amp gauge as they used with the 60amp alternators. The shunts were brass sheet metal pieces that bridged the amp guage terminals to compensate for the higher amps due to the larger guage wiring that bypassed the bulkhead connections, and the increased amp output. I am using a Denso alternator and brackets from '90's Dodge van that is rated at 120amps. That's why I am looking at the use of shunts. Granted, I could modify tha amp guage in my rallyy dash cluster. But since the factory made it work on pickups for a number of years or fleet/service trucks I thought about finding out why it's not the preferred method when upgrading to a bigger alternator to run newer accessories. What I don't know is what size shunt, and if I am just barking up the wrong tree!