Micro Switch 63SC35-1 prototype
The photos below are archived from eBay listing 223782018077 “Rare 1970's? Micro Switch Engineering Computer Keyboard Prototype! No Reserve!” from seller dan123.813; the original listing has since been deleted by eBay. It is an engineering prototype of Micro Switch SC Series model 63SC35-1, with serial number B108.
The use of cylindrical keycaps and apparent low profile of the switches suggests that this was a prototype for the DIN-compliant switches, and possibly the first CT series keycaps, whose patent was filed in September 1981. Although the keyboard has ICs from 1979 and 1980, the switch and keycap styles would imply that this was assembled in late 1981. The keycaps themselves appear to all be labelled, possibly over blanks.