I have a 77 Explorer F100 and I just found a set of original bed rails for it. The drivers side rear corner bracket is cracked and the rubber pad is missing. Might be the same as the right front, not sure. Just thought I'd ask if anyone might have these pieces before I make something to work.
THe passenger front is the same as the drivers side rear. THose corners were used up until the late 90's F series. AS of the first of the year, you could still get them new from Ford. Very pricey, but available.
I checked the corners and you are absolutely right, the left front and right rear are the same. I called a ford dealer who said there were no corners anywhere in the country, but the gasket was available. The computer showed one at a local dealer, but his computer stock said "in a box in attic". Turns out that one wasn't there. Would have sold for $7.68 if he found it. I can make what I have work, just thought I'd start here.