Google is your friend. If you simply search "single mass flywheel SLK320" you will find that Dual Mass is all that is specified.
If you INSIST, just call Rob at Needswings or Josh at The Mercedes Swap Shop and either can give you in-depth answers.

I've been here since 20009, and I can tell you that your question won't be answerable with any certainty here unless Rob chimes in. There is a vast amount of knowledge among those who hang out here, but YOUR question is going deep enough, all you will get is guesses and statements like "... should work".

You MIGHT try this: join MB forums and pretend you have a 2003 SLK320 and ask them. I'd not mention the Crossfire over there, at times they are OK, other times they freak out and bite your head off.