Underdash Harness bunt up

In my 72 Plymouth Duster the underdash harness burnt up pretty good. The ammeter wire basically got several other wires hot and melted several wires. It also melted some wires into the bulkhead connector.

A new harness at Classic Industries is like $700. I can not do that. I am wondering what other years are compatible and if both A and B body are compatible. The care does not have AC.

Also he suggested looking the ammeter in between the battery and the alternator with heavier guage wire and just running that through a grommet in the firewall instead of having it pass everything through the ammeter wire. That seems like a good idea to me. Is there anything to be concerned about there or any tips on that or any of this.

Thanks a lot