Bob,
I wired my '51 but I didn't build a harness in the strict sense of the word. It sounds like you want to layout a harness on a piece of plywood or something, string and wrap the wires, attach the terminals and stick the whole enchilada into the truck.
Wiring the truck one piece at a time, in situ, is also practical and can give very professional looking results plus it's easier than you might think.
Every wire has a 'from' location and a 'to' destination and there really aren't that many when you sit down and look at a wiring diagram. If you are trying to be factory correct then this might not be for you.
All wire sizes are available in modern insulation's and crimp on terminal ends are abundant. A factory wiring diagram will give you proper wire gauge or you can figure it out from the rated load of the circuit. If you take this task a single bite at a time it isn't daunting at all. Good luck.
Stuart
