I know the feeling. There was one on my Suburban when I got it, original owner had out it on when it was a new truck. It was goofy looking, but I really liked the fact that it was kind of part of the truck so I left it there for a year or two. Then on a long road trip out west a truck kicked up what looked like a lag bolt and it broke a huge chunk off the bug guard (thankfully deflected it just enough to go over the truck instead of right into the center of the windshield where it was headed). I took it off when I got where I was going because it looked like garbage and I planned on replacing it when I got back home with another random one I had laying around from an old parts truck, but after having it off for a little while I couldn't bring myself to put it back on, looked so much better without it lol.
As for the paint mystery, it looks like the bed might not be original to the truck. It's possible sometime in the last 40+ years the old bed rotted out/got smashed and was replaced with one from a different truck that was the lighter "tan" color you see peeking through, and the "brown" was half-assed painted over it to match the rest of the truck, and that paint just didn't hold up as well as the real paint on the cab.
Either way, cool truck!
That's definitely a good theory, but it looks like it's the whole bed. Look at the 3rd picture down, the front rail under the back window has the same crumbling paint thing going on, I doubt he had lettering there