James: I started with the intention of using the 1969 donor VW harness and even managed to incorporate a lot of it into mine, but then went wild with a Bosch fuse/relay panel from a Sterling I stumbled across in a salvage yard and mounted it in the trunk.
Then I added a few more 12 ga wires to the engine compartment, "just in case" and extra wires in the front for both fog and driving lights, all driven by relays. In the end, I didn't use everything I started with (and later needed a few more wires in places I hadn't anticipated ten years earlier). It initially took a couple weeks of 2 hours per night, but it got done. I did such a great job on the original version that it's now a PITA to add any new stuff to it, but live and learn - you can't anticipate everything.
My background started in Manufacturing Engineering, so our skills are probably similar, but when I started, everyone was using old-school waxed cord for cable wrapping (I'm still pretty good at it). Now, just give me a tie-wrap gun and stand back.