Ok here is the diagram with the parallel wires on it and the main circuits ( I simply edited the one I already had made )

as you can see I'm posting wich wires will still run throught the bulkhead plug. Honestly no need to eliminate them, but some service on them will be nice ( clean, new terminals if wished, dielectric grease )

the parallel wires will still run up to ammeter studs... why? because when you run the parallel wires, the black wire from ammeter to fuse box won't necesarilly feeds the power from batt, through ammeter, now will feed the power from alternator too ( as far alternator is enough of course ) because so that will DOUBLE the direct and original wire coming from alt through bulkhead.

So we can say ORIGINAL we had one wire ( labeled A ) what it was the only one feeding the main splice originally, now directly the fuse box bar.

The added B wire through the firewall, attached to ammeter, will make we are getting two wires now LABELED AS C to feed the fusebox buss bar from alt . Once again as far alt is enough. If alt is not enough, then batt will feed through ammeter. Ammeter will tell you when that happens, thats its function.

8 or 10 gauge... 10 is really enough if you ask me and will find terminals for it at hardware stores. I fit 8 gauge just because it was one one I had handly from a Coronet 77, but that made me imposible to find a terminal to fit on engine bay side to be able to service that because there is not 8 gauge terminals.

Batt side parallel wire I used a 10 gauge and fit a terminal to attach to a new fuse link. ( 14 or 16 gauge ). The original fuse link it is 16 gauge. Mopar wirings showing parallel wires shows 14 gauge for that parallel fuse link, but 16 will work too without problems. At the end yoiu are also doubling the fuse link, and use a 14 gauge will take too much time to blow in a short problem.

why use a 10 gauge wires if still stock wires betwen ammeter and fuse box and alt and fuse box are 12 ? because teh extra gauge step is for BATT CHARGING moment, safer, not really because the regular car equippment requires MOOORE thicker wires. You are not driving a Motorhome, is a regular passenger car.

Will you use an UZI to hunt rabbits ? everything on the right and enough measure. No need to oversize stuff