The Bosch ZR-6-SII-3320 plugs are OEM replacements for the USA R172 350, the only difference from the original factory plugs in my car was that they had the Mercedes star symbol on them.
If you are interested, here's my write up on swapping out the plugs: http://www.slkworld.com/slk-r172-cl...-ignition-coils-r172-3-5l-v6-m276-engine.html