As far as the headlamp forward harness, you could use the 70, just splice off the high beam leads, lamp pigtail connections are available so you can add the 4 headlamp set up, I've done it in the past, you'll need to lengthen the directional leads also, you'll need the 71 header panel, it is a one year only application, although you could use the 72-4 panel too, but the grille mounting tabs won't line up to the holes. you'll have a little drilling/filling if going with the 72-4 header, Fenders?,...what are you doing?, personally I'd go with the AMD 71 gilled Cuda fenders, lot of BS if your going to weld in louver patch/panels in your 70's,...you'll need the 71 only quad headlight brackets for the buckets onthe fenders to mount the headlights...
As far as the interior, depending on how "correct" you want it, the 71-4 steering column has the key lock tab on the ignition, as the 70 dosen't, the dash pad is the same 71-4 Cuda/Challenger, where as the 70 pads are body/year specific, seats also, depending on how correct your going, tailights, easy swap in, seatbelts changed in 71 also, I know some frown on this swap, but for some it's just another mod, do what floats your boat man!
Your best off listing what you need or have so that others can point you in the direction of parts required
Mike
