I'm pretty sure the C320 is a V6, if so the BH isn't the same. The 4 cyl 95 - 00 C220 C230 and SLK230 are the same though I'm pretty sure they stood the motor up at some point post 01 so the shifter would be in a odd place.

The M104 ( 24 valve head ) is the same basic block as the M103 ( 12 valve head )