I have a 74 Dart Sport and I want to move the rear bumper in closer to the body. I just bought a set of 70 Duster rear bumper brackets. I am thinking that I should just put a set of aar fiberglass bumpers on it to save weight. My question is that aar lists the 70-72 duster bumper different from the 73-76 Dart. What bumper should I be looking at to use with the 70 mounts to bring it in to the body closer?