The original post with pictures disappeared. Could you re-post them? Also higher res pictures including front and back of sheath would be helpful. 1960 seems to be right... Ron nailed it...but then again he is good.
Incidentally, this is a "B" sheath. At some point in the 1960s I think Randall began supplying a special sheath with M-16s, no hone pocket, something like a "B", but with belt loop like an "A" and a tie down toe piece like a"C," maybe even throat rivets on some (?) I don't think it was ever pictured in the catalog however, just referenced.
Here is the only picture you originally posted that I saved...
