Bulkhead wire 64 Barracuda

Here are a few observations.
I am not familiar with the 64 wiring it differs from my 66, without the bolted connection in bulkhead connector. The 66 has a #10 feed cable from + battery terminal. It looks like the feed from the large post of the starter relay needs attention, the 30A fuse looks like a repair to perhaps replace a fusible link. I added up load estimates, wipers 5A, alt field 3A, ignition 4A, heater fan 8A, headlights 10A, and radio 4A, for total of 36A. So that current could blow the fuse, while running all loads at once.

The HEI ignition has a peak current of 4.6A with average current much less than that, because the current ramps up, just before needed, so it draws less average current than a points and ballast system.

Instead of drilling a firewall hole, some drill the bulkhead connector, and join with a barrel crimp for a solid connection.

Relays are often used to feed under hood loads from direct battery feed, switched by energizing relay with original circuit. One 30A Bosch type relay can be used to power the ignition and IGN terminal of regulator, the relay coil is powered from the point where IGN1 and IGN2 are joined to eliminate ballast resistor. The other coil terminal is connected to ground.

A voltmeter is often used to measure wiring/connection voltage drops in circuits. Drops more than 0.1V typically need attention. So measuring may save time, by not fixing what is working, and verifying improvements.