The JRB "appears" to be made for a Model #4 or something similar. What is puzzling if the "1"-6 on the back of the sheath? I think it's earlier than 80's, ranging over the 70's decade, probably early-mid, judging by the wide throat.
If Maurice Johnson had "specifically" made the sheath for Ralph Bone, an impression of a dog's "BONE" was normally stamped into the sheath...just sayin',
Stay Sharp, Capt. Chris