In case you’re curious about some keyboard history, I just finished scanning my copy of the first edition of the IBM Keyboard Operator’s Guide from December 1992 (SA40-0749-0, P/N 1370430).
It’s not an in-depth technical document (as the title should imply), but it’s still a cool snippet of history and will give you an idea of the documentation IBM once supplied for its Model M keyboards. One of the more interesting things about it is (if I’m not mistaken) is one of the earliest references to the IBM Model M5-2 (Model M with an integrated trackball on the top-right corner) keyboard.
Enjoy! 
