I have the same rear bumper as you do, no depression. I'll have to double check because since the truck is modified, I don't think I have as much room between the bumper and bottom of the tailgate. I bought the front splash apron that fills the front bumper and grille area and I couldn't fit it in there. Not sure if he modified the depth of the bumper or not. I really need to post pics. I might just have to drill a new hole under the tail gate. There's 2 already there for the current size license plate CA uses. I bought these 51' plates and they're cost me a pretty penny since they were clear to register and are in awesome original shape.
