Joe Cohn forwarded some additional pictures of his low-S m8-4. I hope to get some more later. If so, I'll add them to this post.
My 3-7 circa 1960-61, has an interesting feature visible looking at butt of handle. There is a seam down the middle, as if the handle was originally in two parts, see picture below. None of the other Delrin knives I've seen have this feature, they all appear to be a solid piece of Delrin ... So the seam in the old 3-7 could have had something to do with experimentation with the material early on. I assume that only the "SS" knife and this one of Joe's might have that feature.
Joe sent me a picture of the butt of his knife and no seam seems (yuk yuk) to be visible... so I guess the feature of the 3-6 is unique...
...which raises an interesting question. Just how does the shop make one-piece handles, wood, Micarda, Delrin, horn, etc.? Do they drill a hole in the tang, and then use a rat-tail file or something to shape it to fit the tang? Never really thought about it...