Re: '69 RS Wiring harness
Yes, the gauge and non-gauge harnesses are different,but RS is not, except for the rear harness which includes the backup lights. The RS system is vacuum,so the wires should all jive up front for you. Not sure which part of the harness you are trying to work a deal on, i.e., complete harness, underdash and underhood,etc. For a frame of reference, a completely new harness from front to rear is roughly $500.
FWIW, the used harness would have to be way cheap and in perfect shape for me to consider using it. Had a bad experience once with used wiring in a 55 Chevy. The car darned near burned to the ground,and could have taken the house with it. Never again. Its new wiring for me. The peace of mind is something that's tough to put a pricetag on.