So the 73 style would be longer?At least two things that I know of. Seems like the earlier version is more of a solid bar style and holds the bumper closer to the body. The later version is a molded steel plate that increases the distance from the bumper to the body due to safety concerns during an impact/collision. At some point there was an addition thick steel plate that followed some of the contours of the bumper added between the bracket and bumper. There may also be a different bumper bolt pattern too.
I have a 73 Chally, so my response was based upon that. I'd say go ahead and use the search engine on this site and type in bumper brackets for the early and late year models. I think you will see the difference.So the 73 style would be longer?
What about the front?View attachment 91140Here is a picture of my dad's 360 Cuda which has the stock bumper brackets. You can see how Mopar used filler pieces to cover the gap that was created by the bumper brackets being manufactured to move the bumper away from the body. It really is pretty ugly and a lot of people will put on 70-72 brackets to move the bumper closer to the body.
So could a set of 71 brackets fit on a 73 body?73-74 used 3 bolts into the frame rails 70-72 only used 2 .
On my cars I always modified earlier brackets to fit & pull the bumpers in flush .