FWIW. I see the original thread talks about the stock CLK320 airbox setup as a good performer. I went through several designs, first using a C36 airbox, which didn't match up to my MAF, then I purchased a full CLK320 airbox for comparison, the top section is almost the identical size, but the bottom section was more restricitve than the bottom section of the C36 airbox. So I Frankensteined the airbox, using the OE top section and the C36 bottom section (with a K&N). I am quite happy with the final results, although I don't have any before/after dynos with the different air intakes (too much time spent on the dyno with the C32 injectors and Unichip piggy back ecu). End result, 270 rwhp.
The bottom of the C36 airbox has a larger secondary intake than the factory CLK box, plus the mouth of the box is also larger and thus can flow more air.