If, as you say, its from a 2006 model then its from a W164 and it will not fit your W163. That's obvious just by looking at the size and shape.
I won't comment on the merits of hacking holes in the dashboard of a W163 to accommodate a free head unit from a W164. Each one to their own.I am aware that its larger than my original factory unit. But I believe modifications can be made to make it fit. Like relocating the ESP and fog light buttons and of course widening the hole for which it will be mounted in. I got the unit free from a wrecked 06 ML350. Eventhough the truck was damaged badly. Once I pressed the power button on the command it did come on and work perfectly. I also have the vin from the wrecked ML so I think the command code can be acquired from the dealership. The only problem I believe I will run into is, this unit has two fiber optic wires that I believe runs to the factory amp, my car and amp only has one fiber optic wire. Thanks guys.