The only K-bus car to come with it was the E38 ECE, so used parts are very limited. A new radar is thousands.

I would attempt it on a US E38, but no way on the E53. A major part of ACC is the DSC III system which we do not have. I don't recall seeing any provisions in our DSC system coding for ACC or even DCC last I checked. Not to mention, there isn't anywhere to mount the radar properly.