Greg, I think you have found correctly. I have not seen anything for the front cab sections to fit our 57-60 models, except for floor pans, and the floor reinforcement piece that goes from the floor to the step riser.
I have been looking at the 61-66 parts for that same area and I have a guy here that has a 62 and I am going to get with him to make some templates to see if the later model pieces will fit, or can be modified to fit our trucks. I need some of that metal too for my 57 and it would, might. be helpful, if not too expensive, to have stamped pieces we can use.
I will post my findings when I get together with that guy and do measurements, pictures and templates.
Greg if you are talking about the boxed in area just below the lower hinge. I looked also and ended up making my own, it was not too hard but then again my don't look original. Should be pictures in my albums. If you can weld in store bought panels you won't have trouble building these parts. Look at it as a chance build your skills.LOL
Good luck in your quest!