Question on Big 3 Upgrade for OBS Truck

[Acropolis]

I understand the logic behind the Big 3 Upgrade, but I had a quick question. I have an '88 5.7L. I understand the ground wires. I also know that I need to run a wire from the alternator to the battery. Currently, I have a wire that runs directly from the battery to the starter instead of the alternator. It also has a second wire running along side this wire that continues to somewhere behind the engine block that must power the electrical accessories on the truck.

This is where I need the help. I am planning to run a wire from the alternator directly to the battery. A second wire will branch from the positive terminal of the battery to the starter. What I need to figure out is where to run the wire from the battery to the power distribution block. Where is this wire connected? I also assume that the current wire running from the alternator is going to the same place since it doesn't go directly to the battery. Is this correct?

Acropolis

[Acropolis]

OK, I tracked both wires down to the block on the firewall. I'm guessing that if I run a wire directly from the alternator to the battery, the wire from the alternator to the block can go away. I then just need to upgrade the wire that runs from the battery to the block.

What gauge wire should I run from the battery to the block on the firewall? Does it need to be fused (the original wasn't, but some people have mentioned that you should)?