remove that brown cover NAW!!!!!!!!!!!!!!!
not really know the exact detail, but just telling what i know....
first gen is KMAC LE (not a real success as anodizing failure, upper and lower casing color mismatch and weak anodization), have winkey and winkeyless
improved with KMAC (improved anodization, but still soft anodization, not hard anodization) have winkey and winkeyless
then KMAC mini? a 60% board with arrow cluster and 12 Function buttons at left hand side
then KPAD? Numpad for KMAC with a metal bar to lock with KMAC to create full board, not many does that as the color of the kpad and KMAC is not consistent....
now KMAC1.2 and KMAC2? KMAC1.2 is improvement of KMAC (hard anodizing, and no more winkey winkeyless version, replaced with blocks) KMAC2 on the other hand, is new design with no feets, but with slanted body design, again no winkey winkeyless version, replaced with blocks....)
any correction those owners *cough* Kai *cough* YongJK *cough* please add on....

edit: latest ones i think are KMAC Happies, which is like OTD's 356mini's size, but have two layout, either Poker style or HHKB style... hence two types of top cover to choose from...
It's all just keyboard.
I don't own other version of KMAC except kmac2, just by reading I am also not too sure the details though.