Easiest way is to open the hood and the valve cover will tell you all you need to know. It will say "MERCEDES 2.3-16" very clearly. Otherwise, any other 2.3 is the 8 valve.

The 16V is highly desirable as a performance sedan and as an interesting part of Mercedes history. It does have its quirks, like the SLS rear suspension, dog legged Gertag 5 speed, parts costs and making most of its power closer to redline.