| Standard 56" 6-rib belt, every manufacturer has their own part number.
You are making a huge mistake making billet pulley. First off, the hub wall thickness is limited by the space that's there. This is a stress point and make it out of aluminum weakens that area significanlty. If the pulley snaps at the hub, it will damage the crankshaft. The other risk is you are eliminating the harmonic balancer that's part of the factory pulley. I don't know the long term risks involved but MB engineers put a harmonic balancer in their for a reason and it must have been significant of a reason as car manufacturers pinch pennys when it comes to parts of little or no value. | 
