Don, the i - 'reverse' j substitution is pretty much common knowledge, so it is not described in that many sources (after all, who would describe the alphabet in English, for example?).
Capital J and Capital I are hardly distinguishable in old German, and as the old text shows, the i and j were regularly substituted. I may have some examples amongst Mauser's own handwriting, have to look into that.
It would be fun to see a logical alternative for the 'Lj.' abbreviation, though. I really can't think of anything else that would make sense, unless the 'j' was actually meant to be an 'i' and we are looking at an 'Li' abbreviation instead...
Don't you just love old German
But how about the abbreviations used by the Royal Württemberger Landjägerei? They were quite small and there are some examples of the use of K.L.K. and L.K. markings (Königliches Landjägereikorps / Landjägereikorps). This was a relatively small corps which was called Landjägerei before and during WW1.