After a bit of web searching I was able to identify the fuse box as an AutoWire Power Plus 13 unit. This helped a lot as I could now understand how the wiring was supposed to be routed and I could then figure out how it had been modified and actually run. I did make a few changes, re-wired a few circuits, upgraded the wire gauge in a couple places, and added the necessary circuits for the electric fans, the new sound system and the tonneau cover brake light.
I don't have any pictures, but I did create a wiring diagram shown here (mostly for my own historical record and future reference). There are a couple wires/circuits that remain unknown because I didn't need to trace them. At least one has to do with Vintage Air air conditioning unit.