What do I need and what do I don’t!

Love to find an example where an ammeter in a '75 actually caused a fire.
I had a '75 4 door Valiant and it did not catch fire. Not even once.
Headlights tripping circuit breaker, yes, and that was pretty much the only electrical problem with it.

If the OP's car has the seatbelt interlock, then there are simpler ways to permanently bypass it.