I wrote to Jeff Armstrong about the LK201 ... and he replied:
"I'm not personally aware of differences in LK201 keyboards. In my experience, as long as the business end of the connector is compatible, it hasn't mattered. In fact, I often use LK401 keyboards with my Rainbows just because they're considerably smaller.
LK keyboards have been emulated before, I believe. You might want to look at the SIMH package. There was a gentleman whose name eludes me at the moment who managed to create a DEC Pro/350 emulator derived from SIMH package. I would guess he had a reasonable simulation of the LK series. HOwever, I would not be surprised if they were emulating the serial LK interface rather than the internals of the LK itself."
The emulator he mentions now is really interesting and can be found here ... http://xhomer.isani.org/xhomer/
the machine would make a nice addition to MESS.