E body Rallye Dash Harness HELP

Currently working on the final steps of my dash assembly for my 71 Challenger. It has what I'm pretty sure is a 72 to 74 rally cluster that I had redone and I'm now trying to get a under dash wiring harness ironed out. The car came with 2, (6 years ago) I opened my boxes and it turns out one appears to not be useable, the other I believe is for a standard dash. Looking at buying one, but want to be sure I buy one that will work. Can anyone provide a part number of a harness? I see number stamped on fuse blocks, but need help identifing what I need. Single speaker with a.c..or...what numbers will work? Also see conversation kits for sale??? These work? Thanks in advance...

m&h electric best you will find

M&H is the best if you want a factory correct colored wire and factory like connectors. Year One I think is still the only place to buy M&H. They have a 30% off coupon this weekend. Use BBQ16 code.

Thanks for the tips! Appears to be good route...