Are these bed bolts OEM 1970?

[Gromit]

Last week I decided to change out the eight bed to chassis bolts in my 1970 C10 Fleetside with a steel floor long bed.

It didn't at all go like I expected. I was ready for the worst, but all the nuts came off without too much trouble.

The next surprise was the two bolts closest to the cab were sized 7/16ths instead of being like all the others 3/8ths.

Then I noticed the old bolts seemed to have rolled threads (as opposed to the cut threads on the new ones), that were fully 1 mm larger than the bolt shank - and moreover seemed to be made of better steel than the new bolts. I don't really know that the old ones are better steel; but when you bonk the old ones together they make a nice "Ding!" sound - where the new ones make a dull "thud."

So I decided to restore the old ones (using an electrolysis setup), and put those back in instead of the new bolts I already had.

The other thing about the new bolts that sucks - they are threaded all the way up the shank instead of just the lower 1-1/2 inches or so.

Anyway, the reason I need the forum is to ask if anyone else has these 7/16ths diameter bed bolts with rolled threads that are marked with an "E" on the head?

The other six bolts are 3/8ths and those are marked with the "R.B.W." that I have seen elsewhere on fasteners on this truck - so I am pretty sure those are the originals so no mystery there; (though I would like to know who that manufacturer was).

I tried to look at Brothers Trucks and LMC but it looks like their bed bolt kits just use all 3/8ths and don't have the two larger 7/16ths bolts in the front two bed floor holes.

Photos attached..