Take a look at a '69 harness. The alternator is on the right side and I think that the firewall connector is the same style. Just be sure to match up the individual wires so there are no cross-connections.
They are not difficult at all to install, just a little tedious getting the wires fed through the radiator support and across the front.
Be careful to really think ahead with your project as even small mistakes can lead to big problems. Good luck.