I'm guessing Johnson sheath, with out seeing the back of it. Heiser was almost history by this time, but it could be a Heiser. Stainless steel blade (Pre "S" trademark stamp on those Model #10-s) I would venture late 50's or early 60's. I believe the micarta is black and just showing it's age. Best I can do with the photos presented and, of course, not having the combination in front of me. There will be some more pipe up with an opinion, I'm sure.
The split loop, on the front, under the handle may have the maker's name. It could say "Heiser and have the "10" for model and the "5" for blade length in seperate locations, above and below the split loops.
Best, Capt. Chris