From your pictures it looks like a lost cause. I suggest selling it to me cheap and get another.

Just kidding of course. I have bought a lot of body parts & patch panels from American Classic Trucks and have had some fit good & some that need to be "altered" a little bit. They all need a little customizing I think, no matter where they come from. I have heard Dynacorn makes pretty good panels but have never used them. If I can save a few bucks I don't mind a little cutting/welding/filling.
It is hard to tell from your picture, but if you wanted to replace the back panel because of the right cab corner I would straighten the panel before replacement. Maybe repair the dented area and just replace the lower corner secton. The back panel is about $400 plus shipping and a lot of work. The lower panel is $26.00 & about $15.00 shipping, and no where near as much work. You can check my Photobucket link and see where I have replaced the lower sections.