71 Duster Bumper on 74 Dart Sport?
The 70-73 rear bumpers are the same shape but the 72-73 has those vertical slots for the redesigned bumper jack that eliminated the outer hook.
To bolt it in, the brackets will work but the mounts on the 74-76 cars need modifications. Those cars has a big hole in the flat mounting surface where the 70-73 bumpers would normally mount. The 74-76 year model cars had that fore/aft shock absorber that went through the rear body crossmember. You just need to weld a patch over that hole, then drill smaller holes for the mounting bolts.
I did this when I converted a 74 Duster to a "70-71" taillight design.
The 70-73 rear bumpers are the same shape but the 72-73 has those vertical slots for the redesigned bumper jack that eliminated the outer hook.
To bolt it in, the brackets will work but the mounts on the 74-76 cars need modifications. Those cars has a big hole in the flat mounting surface where the 70-73 bumpers would normally mount. The 74-76 year model cars had that fore/aft shock absorber that went through the rear body crossmember. You just need to weld a patch over that hole, then drill smaller holes for the mounting bolts.
I did this when I converted a 74 Duster to a "70-71" taillight design.