[unruhjonny]

I believe that the 1974 & 1975 bumpers and bumper covers interchanged;
I believe that original 1974 bumpers were made so that the "bumperette" portions could be unbolted, while the 1975 bumpers couldn't.
The biggest problem with 74/75 front ends is the rubber filler between the fiberglass upper portion and plastic lower bumper cover.
If my memory serves me, that filler became a part of the 1976 (lower) rubber bumper cover.
The upper fiberglass header panel, although quite alike, differ slightly between 74/75 & 76.

I also believe that the 1976 though 1978 bumper under structure (and filler) interchange even though the cover was 1976 & 1977/1978.

I also believe that (for clarity's sake) the quarter panels, trunk floor and rear sheet metal are the same for 1975 through 1981.

depending on where the car is from, the rust can start in different areas - but generally inspect the rear leafspring boxed frame sections under the floor, and then inspect the frame rail as it goes up the rear wheel well, and to the rear tail panel;

Also inspect the rockers, especially where they connect to the quarter panel - there was a rubber flap at the wheel well that could get stuck closed, and then cause debris to collect, and start the rotting process.

After those, there is another rubber flap at the fronts of the inner rocker - this one could get stuck, and cause debris to collect there - in addition to this being the front rocker drain, it is also the front cowl drain.