So after hours of searching I finally found a damn manual for the FC660*C* which I assume, in terms of DIP functionality is the same as the Mechanical switch counterpart.
Sadly the capslock DIP switch is to ctrl and not FN as I wanted, so now I need to ask about HASU controllers.
The FC660C has a hasu controller, I think I heard somewhere that this does not work for the ''M model, is this correct?
*I would also be using the somewhat rare ISO version which I maaay be a double no depending on how HASU controllers intercept/interpret key presses...?
The FC660M seems to be a good keyboard, fan of the solid looking plastic body construction, 2-tone color scheme. But the nearly impossible to find in stock ISO version and lack of even this minor reprogram-ability is potentially a killer :/