I have the CDA 9820XM installed in an '81 300SD; it's a DIN fit, so the car doesn't matter. I've been happy with it so far (1 month). If your antenna works and you're happy with the installation, definitely reuse it. Otherwise, I had a very small Terk antenna fitted at the base of the windshield/front of the dash inside the car, and I've had no problems with reception. It's very clean, the cable runs inside the dash to the back of the unit.

Note that this unit plays CD's and CD-R's, but not MP3, if that's important to you. Also note that the unit comes in both silver and black; specify black if that's what you want (I assume it is). I didn't specify, had only seen a picture of the black unit and didn't know there was a silver option, which was what I ended up with (the circumstances precluded my waiting around for shipment of an alternate unit). It looks OK, but I'd definitely rather have the black with any MB. Also, Alpine has an optional external input (you have to pay extra for it, not much though) if you want to run an MP3 player. I ordered that, and had a small jack installed in the console tray under the stereo where I plug in my IPOD. It works perfectly with the head unit.