OK, as it is right now I have the red 12 gauge wire that comes from the starter relay straight to the fuse block from the bulkhead connector,connected to the batt feed terminal. Can I just cut that wire and splice in the ammeter? I also will run the parallel wires to the ammeter.

You are correct, it is a heater only car, no AC.

I will attach the power wire for the headlights (black w/white tracer) to the black side of the ammeter, as you suggested.

The dimmer for the lights, I will connect the tan and the 2 orange wires together, and splice in a fuse. I would rather use the fuse for the coil, as directed in the instructions.