The torque boxes weld to the frame to make it more rigid. You can find them at Mancini.
Some other stuff that comes to mind (that hasn't been mentioned yet):
- The AAR front and rear spoilers! (It's not the Challenger TA spoilers, those are different)
- The rear trunk lid has sqaure-shaped holes cut in the bottom for mounting the rear spoiler
- You'll need the hood pin brackets and pins for that fiberglass AAR hood
- Don't forget the classic fog lights on the front
- They have the rallye gauges (4 big gauges)
- Front and rear sway bars
- Rallye wheels
- The rear valance doesn't have the exhaust cut-outs
- Aren't they all 4-speeds?
- I think they might all have the 6-pack style side-ways mounting windshield wiper motor
- I'm pretty sure the windshield washer sprayers are unique
- I think all of them had painted side view mirror(s)
- The center console has the ashtray holder (like all 70's, just thought I'd through it in)
That's all I can think of right now