If you are going to replace the factory wiring, do yourself a favour and just get reproduction harnesses. I am trained as an auto electrician, have my own small classic auto repair business and I can't tell you how many times I get calls about wiring a car using a painful (painless) wiring system. They are crap. They have no harness disconnects, they give you a bunch of rolls of wires and expect you to know what to do, and their fuse panels leave much to be desired as they are one long bank with predetermined amount of "hot, acc, and on (running) fuses (when they get power).
1966 Mustang Sprint 200--Wimbledon White
1998 Mustang V6 Coupe--Silver--RIP, Totalled by brother
2005 Mustang V6 Premium Coupe--Sonic Blue