I may be different thinking, than others, but I just have a problem using old wiring, when there is some new stuff available. Yeah, it costs a little, but in my opinion, what is under the hood is subject to all of the heat, cold and vibration that exists when the vehicle is being operated.
If you have a 1-wire alternator and and HEI, you will have to modify both the engine and lighting harnesses. I have used stuff from
www.wiringharness.com, and they will make them the way you need them. They have all of the right connectors and the wiring color code matches the original colors. The stuff just plugs in and hooks up just like original, and you don't have to worry about brittle insulation, broken connectors, splices, etc. It will add to your peace of mind, when you need to count on it running for a long time.