Burned bulk head connection

Crackedback came up with a simple plan on this. You make sure what is "originally" there is in good shape and then run a fused/ breaker protected wire direct from the alternator to the battery. This turns the two wires that go through the bulkhead into a feed into the interior, and relieve that end of things of the charging current.

If you want to keep your ammeter, that gets more complicated. You really need to upgrade the wiring size. The ORIGINAL cars which came with heavy duty 65A alternator HAD a sort of factory bypass. They ran the ammeter wiring through separate gromments in the firewall. You can look this up in some of the service manuals over the years.