At a recent car show, i was parked next to a 73 Challenger with my 74. The REAR bumpers "looked" identical to the eye, and measured the same width height etc. Then I measured the bolts, and found about 2 inches DIFFERENT on the inner bolts. So obviously the brackets are different.
So, if i decide to spend the money on a new rear bumper, I guess ill have to buy new brackets that match the year of the bumper I buy. Re-chroming is way too expensive.