Hi Dave, Great find, beautiful kniffe.
From my recollection the 124/122 came into production in 1967. The 124 was named the Frontiersman, and the 122 was called the Nemo. The first runs of these knives had white teflon spacers and then Buck moved to the red micarta spacers evident on your knife. The guard and pommel are stainless steel, the handle is black phenolic, and the blade steel is 440C stainless. The knife went full tang with micarta scales and two SS pins in '70 or '71. Some were manufactured with partially serrated blades.
As to your question, is it a 122 or 124, there was no difference between the two knives. The 122, Nemo, came with the scuba plastic dive sheath and the 124, Frontiersman, came with the black leather snap-over sheath. The box the knife came in was the same except the box was printed with: 122/Nemo and if you purchased the 124/Frontiersman the box had a gold sticker covering the Nemo designation and stating the knife was a 124/Frontiersman...(does that make sense to you?)
I've got a couple of 124/122's similar to yours. I'll try to post a pic of the first issue with the white teflon spacers.
Any and all corrections/clarifications by Buck xperts are welcome...
Thanks Mike. Now the hunt starts for a scabbard.