Manuals can be found online for this camera by searching for the Kalimar Reflex CTL 2000, unfortunately, not for free. But that might be the best place to find an explanation.
http://camera-wiki.org/wiki/Regula_Reflex_2000_CTL for those unfamiliar with the camera like me.
I suspect the notches are for a locating pin on a mount plate, be it quick release or fixed to a tripod head, for a tripod made by the same company or contracted by them.
Yes, but as I indicated in the first post there are some points that make it enigmatic...
King was a manufacturer known for their middle-class cameras, and these are quite frequent here. Also known for their electronic flashes.
They also made higher-end cameras, that are much lesser known, and that I have not come across.
Initially I thought the 2 you first posted were just oddballs, but after looking at (the few) images I could find showing the bottom, it seems most/all had this contraption.
Seeing how it was also sold as a Kalimar, I would tend to agree with shutterfinger that it was for a proprietary tripod, made (probably) by Kalimar. It certainly is a mysterious piece!