For the CARK-91, you can either get a dash-mount bracket which clips behind a dash panel, and will not involve any drilling, or you can get the MB Original Console - again no drilling, and mount the phone kit on there. - you can get a lead from dash-mount to fit between the car kit and the ISO Connector on your stereo, to make wiring etc. much easier and have the phone played through your audio speakers.
I think fuzzer is fitting one to a W210 - so might be worth asking him for any tips he has !