Hi Ryan, I just fit up a rear bumper and brackets that came from Chevy Duty. They came with the truck when I bought it. The PO bought the parts but never installed them because he said the brackets didn't fit. True, they were off by quite a bit. Once they were mounted to the frame I used a big old crescent wrench as a lever and simply bent it around to match the holes. It’s amazing how easily the brackets can be bent. One thing you might want to do before installing the brackets is to round off the edges to make them look more like the original bracket material.
Once the holes were lined up with the bumper I bent the last couple of inches by heating the bracket till it matched the general curvature of the bumper as close as possible. It’s impossible to get the contact area perfectly flush or to match the compound curvature of the bumper. What you want is more or less a 2” square pad that contacts the bumper.
Like our member from Yakima noted, chrome plating won’t bend very much so you don’t want to synch up the bumper to tightly or it will pop the plating. I installed a thick layer of gasket material between the bracket and bumper. They used this in mounting the parts of the front clip or running boards and called them anti-squeak gaskets.
Denny Graham
Sandwich, IL

Denny G
Sandwich, IL