Alot of the decision making has to do with the engine you are going to install. A carb'd engine is much easier, especially if you've got a internally regulated alternator, although you can delete the relay board if you have a externally regulated alternator and mount the regulator elsewhere.
Another issue to consider is the fuel pump relay. If you've moved the fuel pump and aren't using the original fuel pump circuit, then you don't have to deal with this.
There is a factory connector that will plug right into the existing harness, but the connector and pins alone costs $45!
I do custom harnesses for six conversions, and sell DIY kits. I use wiring with color coding the same or as close as possible to factory. I also use black PVC jacketing and heat shrink for a real OEM appearance (I HATE black electrical tape wiring harnesses
). PM me if you want more info on what I have to offer.