I just went through that decision process myself, for a '48 2 ton.
After checking the usual on line Chevy parts suppliers I had the options of stock reproduction without enough wires, "updated" harnesses with PVC and too many wires, or have a custom harness made.
I went with the custom harness.
The changes to the main harness were a 1 wire alternator so no regulator and since it has a 90A output, Ammeter replaced with a voltmeter. Fog lights, fender mounted directionals, a cold start circuit and a horn relay.
I went to Narragansett Reproductions, a company known for doing high quality harnesses. Original wire styles, factory color codes and connectors.
I even bought a new directional switch from them since they remove the PVC wires and install the proper cloth pigtail.
The main harness was around $580, Chevy of the 40"s lists for $715.
The rear body harness was separate. I sent them a drawing for that and haven't gotten the quote yet. That had a branch for the auto trans backup and starter safety switches, dual tail lights, separate directionals and backup lights, and the gas tank along the frame rail. It is a long wheelbase 12' stake body.
