I found a few threads on the subject but no definitive answers. I had a chance this weekend to compare the two side-by-side and take some pictures.
It looks like the shape of the bumper itself is the same. But there are two major differences in the brackets. First, the 73 not only uses the well-known hoop bracket but also gets rid of the 72 bracket in the process. Second the side bolts bracket sticks out further on the 73. This makes the 73 only usable with the hoop. It would take a lot of fabrication to rebuild its brackets to 72 shape and look.

It looks like the shape of the bumper itself is the same. But there are two major differences in the brackets. First, the 73 not only uses the well-known hoop bracket but also gets rid of the 72 bracket in the process. Second the side bolts bracket sticks out further on the 73. This makes the 73 only usable with the hoop. It would take a lot of fabrication to rebuild its brackets to 72 shape and look.


