I am working on a 70 Challenger. It has this cluster in it. I didn't install all the wiring. You may be able to use the factory wiring. This car is using wire from this company. http://www.americanautowire.com/ It is a nice set up because it updates all the wiring for use with modern gauges and accessories.
I'm using a harness from the same company. Are you running a one wire alternator as it calls for? I'm debating it since I've got a new 85 amp alt, hate to spend the xtra cash for another new one.