Hey Geoff, are you 100% sure about this one?
I think that "this" 378242-S is correct for the early years, but I do think that the Bronco received the later style smooth Sems dog point hex washer screws (at least by 1973.)
As is typical with Ford, and with the MPC...superceded parts with the same form, fit and function will often be deployed as a running change and keep the same part number at the same rev. So at one point in time, (like 1969) you might have a serrated fastener, but in later years...a smooth one. We see it a lot with fasteners on Mustangs, and so I had to go check my tire carrier from my Boxwood Bronco. Sure enough, it uses a Hex Washer SEMS with leadpoint, but it does not have the conical tooth washer.
I believe it is the same part number, but a visually different part. I think this is why AMK sometimes gets it "wrong." The ONLY way to know is to look at period correct examples from similar builds in similar plants.
As I recall, the tire carrier hinges were installed prior to paint. So the "seam sealer" is the primer and paint. Bolt heads are painted body color, and under-surfaces end up rusty. It's always disappointing to see really nice Bronco builds with unpainted fasteners, or fasteners that get painted, and then "wrenched on" after a coat of color, and 3 coats of clear! Those idiotic philips head fender screws come to mind...Or my favorite, the (1) serrated ground screw on the instrument cluster...
Nobody is out there building Concourse correct Broncos. But someone is going to judge a Bronco to Thoroghbred standard someday, and I don't want everybody "feeding their cat from a saucer."
James.