First order of things would be to get to the mercedes EPC. You need to make sure the chain setup is the same as the us model 500SEC or SEL. I'm pretty sure it is. Then go to parts sites to find your part as you were ordering for a U.S. Model Mercedes. 81-85 m117 500sec. Its possible the 560SL is the same as well. Labor is a lot. I would count on at least 10hrs from an experienced mechanic. There are a few replace while your there items like the water pump as well.

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Chris
84 280sl
82 300d euro