Hi Rhino, thanks for the answer. I haven't event bohtered to compare how many keys are on these two, and this certainly defeats my idea of swapping keyboard modules between K1 and K4.
Why? I was searching for working K4, and found one that seller claims it's working via MIDI, but it has no keyboard module for some reason. On some other auction site i've spotted broken, but visually intact K1, and idea of buying these two and donating keyboard module from K1 to K4 came to my mind.