Diagram B is exactly what I did on my truck. The volt gauge is just using 12v from the fuse box and a chassis ground.

The Red/Black splice near the ammeter is just the two ammeter wires disconnected and tied to together. Where they come through the bulkhead connector is just removing the connector and using a continuous wire through it. The bypass is just a wire run from the Alt + terminal to the starter relay + terminal.

The mad link above is pretty easy to follow. The key is making good connections. If the wire looks questionable replace it.