The dr diff kits had a 1" offset front bracket, with 2 spring height holes and a 3/4 offset rear shackle. I had no issue with the valance on cudas with stock length springs. He used to sell a 1.5" offset kit that some said would hit the valance, it used the same front hanger and more offset at the rear, as e-body springs are in the car at an angle. I would measure the valance now and see how far you can go, then call cass, aka doctor diff. I put the 1.5 kit in for a guy 12 years or so ago and he never said the valance was a problem, but he also was a bodyman so moving the cuda valance bulge over would have been easy for him.