72340, It can be done but you will find a few differences. The brackets for the tail lights, and a couple other brackets back there. I think I may have a set if you need them. Also, the back edge of the trunk pan is different. On the '72 it is straight across the back, on the '74 that back edge has a couple "indents". I used a '75 trunk pan in my '72 and just used a couple thicknesses of sheet metal welded in to fill the gap. Worked fine.
I can't address the bumper issue, but I don't think it would be a problem to use a '72 bumper and brackets.
C
You might want to try Auto Metal Direct if you are wanting to do that. They have the '70-'71 tail panel, reinforcement brackets, and tail light brackets.