The bumper filler panel or valance is often called a splash shield or splash pan. The panels that cover the gap between your runningboards and bedsides are called aprons.
The other shield(s) I think you may be talking about is called a stone shield. If your 53 is like my 50 GMC there are 3 of them, with the "sloped" panels on the ends and a more rectangular panel in the center. I've never seen them in a catalog, on ebay, or anywhere else.
