Someone school me on 73 Duster rear bumper.

Hello all,

I have read the posts pertaining to changing out bumpers on 74 and later Dusters and have questions.

Is a 73 rear bumper the same as 70-72 with the exception of the extra reinforcement?

Why when a 70-72 bumper is put on a 73-74 Is there usually a gap between bumper and 1/4? Since the 1/4 panels didn't change in that location it would seem to me if the proper bumper brackets are used, an earlier bumper should sit flush all the way across.

What am I missing?