Wiring harnesses

The ammeter is the same for a late 1972 to 1975 Valiant. [per Motors manual]. The 1976 ammeter is a low current unit for the 1976 shunt wiring system ONLY. Your car can handle a 40 amp alternator safely. Anything over that and it may cook the firewall plug connector when the battery is low and charging a lot. There are ways to correct that safely.

Not sure why you'd change out all the wiring in the car. Usually , the underhood wiring gets poor due to heat hardening and oil. The interior wiring usually looks ok and can be repaired unless some wannabe electrician or mice gets there first.