The PO of my truck had put 2x8 steel channel in the frame . He had used the existing holes in the frame. He had added overload springs and a diamond plate bed. I think the truck was a scrap hauler. I removed all that and used the frame boxing plates . They fit inside the frame perfect and we welded them into place. Looks much neater and is just as strong. Its a pretty beefy frame . If its that rusty I would look at replacing it. My 2 sence