The 76 model amp gauge is different from all other models of a-body. No need to do anything to it.
The car has a radio fuse that should handle the typical aftermarket stereo head. Amplifiers require another power supply to their location.
The 76--and a member just sent me an ammeter out of one to play with--uses what is called an "external shunt" ammeter--which actually uses the harness itself as a shunt. This greatly reduces the load on the bulkhead connector, as only the loads on the system go into the interior through the bulkhead. That does NOT mean that the bulkhead connector is completely "OK" but "it might be" And it does NOT mean that you can add a big bunch'a loads that are carried by the bulkhead connector, without damaging it
It ALSO means you might have to do some research on WHERE to connect loads so that they correctly read on the ammeter. One "fer certain" spot is the alternator output stud
So far as a fuse / relay panel there are many ways. You could even go to the junkyard and get one out of a minivan, Jeep or "you'll just have to browze" and then do some re-wiring in the relay panel
