Yes, I saw em on a 73 just Sat, and on 74+, they are truly different its so odd that the little things make such a diff. I take it they were learning the the big bumper stuff then. The brackets are made completely different on the 73+s though than the 70-72 for sure.
The '73 bracket assemblies bolt right into place where the '74 and up bumper brackets attach. It's a bolt on/off swap, I did it. Seth