you can also rebuilt your stock cluster gauge using a factory 60 amps unit and install the ammeter face from your D100

https://www.ebay.com/itm/1971-Plymouth-GTX-Roadrunner-Dodge-Charger-Super-Bee-NOS-MOPAR-Ammeter-Amp-Gauge/330851585796?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2055119.m1438.l2649

althought can't recall if the D100 cluster is with needle pointing up or down. studs gap uses to be the same in all Mopar ammeters

then install an underdash voltimeter