I figured I would post this as I just finished converting the rear bumper on my 1974 Challenger to a 1972 style bumper. The conversion is pretty simple, requires no special tools or body modifications and brings the bumper back in tight to the body for a cleaner look IMO.
To do the conversion you will need the following:
-1972 Bumper (I got mine with Jack slots, made by AMD)
-1972 Bumper Brackets (I used AMD)
-70-72 Challenger RR Bumper Filler (Classic Industries #MM1256)
-70-72 RR Bumper Guards (Classic Industries #MM1106)
-70-72 Challenger RR Bumper Guard Brackets (Classic Industries #MM1790)
I'm sure their are other places to get the parts, I use Classic Industries because I live close by and I'm impatient... Once you have everything, start by removing the license plate, then remove rear valance panel underneath the bumper. There are screws on the side and along the top as well as two screws in the bracket behind the license plate. Next take off the existing bumper guard bracket which is bolted to the frame above the leaf spring. You should then be able to unscrew the bumper and remove it. Once the bumper is off remove the bumper brackets (two bolts for each). You will next want to unscrew the plastic spacers and remove them. You should now have the lights refinished and the back painted, etc. etc. because why not, right...
OK so once you are ready for reassembly, the first thing you want to do is make sure you have filled in all the holes from the plastic spacers, as depending on where they are, they will show when you are done (I learned this the hard way...). Reassembly is essentially the reverse of the removal process, start with the new spacer, then attach the bumper Brackets (keep them loose so you can adjust the bumper), then attach the bumper and adjust so that it is even and level and you are using all four bolts. once the bumper is where you want it you can tighten all the bracket bolts and cinch it all down. Next attach the bumper guard brackets above the leaf spring (again leave them loose for adjusting and then attach the bumper guard and top bracket so that the bumper guard is flush to the bumper. When that is in the right position, go ahead and attach the bottom bracket screw to the bumper guard and then tighten the bracket to the frame. Last step is to remove the license plate bracket (upside down V) from the rear valance, use the square nuts in the existing holes on the valance, then reattach the rear valance, license plate and transfer the license plate light from your old bumper to your new one.
Safety wise you are losing the 5mph crash protection so do it at your own risk but aesthetically it looks good...
Attached is a picture of mine.
