Mike...and others,
If you're interested, that is...Below is an example of an early Denmark (Prototype, if you will) with it's proper RMK shop-supplied sheath. Johnson's smoothback pouch-style with no keeper strap!
If you look closely at my poor attempt (It is, after all, Nightime right now) to highlight the back of the sheath you will not notice any blade length denotation. What you "will" notice is the ever-controversial "R-UP" sheath stamp!
For more clarity on this, I also burned up some flashlight battery and dove into The Captain's STASH! Second RMK is an ivorite (Westinghouse, "Old Yeller") Model #8-4".
The sheath, at casual glance looks to be the same,,,,"BUT",,,(Been a while)...The sheath shows the "4" indicating it is for a 4 inch RMK, which the T&B is. You will also notice the sheath stamp, back to it's now accepted "R DOWN" position.
Both sheaths Johnson and, yet, whaddya' know..differences. I hope this helps you Mike in your sheath search.
Stay sharp everybody,
Nighty Night, Capt. Chris