I will need to talk with Mercedes to compare prices but Assenmacher quoted $88 for the gauge. I really don't know how I could be sure of the setting without one. As I mentioned I was surprised to find the loose rocker arms, I had myself convinced it was bottom end.
I'll keep the worn thrust washer idea in mind when I start looking into the ball stud situation.
It would appear that the chain has about 8 degrees of stretch, and along with a number of other things I plan to replace it , guide rails, and tensioner before reinstalling the engine.
I appreciate the information, thanks.