Bumpers on 74 A-body

I put a '73 Duster rear bumper on my '72 Duster. The only difference was that the '73 had in inner heavy steel liner, and rubber bumperettes. From outside they look the same, but the addition of the liner made it stick out only another 1/8->1/4 inch. In '75 the bumpers became massive by comparison - thicker metal, stick out on sides, inner thick support, and shock absorbing bumpers. To my knowledge they never increased in size after that. The '74 I am not as sure about. I know they increased in size over '73, but I can't say it they had the shock absorbers or not.