Vintage Cars: 115.920 engine, piston rings, perfect shape

Question
I have a 1972 220/8 engine number 115.920-12-024144. Here is the problem. I started to rebuild the engine and the top of the pistons are stamped 87.97 or 3.4633 which is .040 over. The pistons are in perfect shape and the cylinders are not tapered. I order rings and now three sets later they are all wrong. The problem is that the second compression ring has a a step in the ring grove on the bottom of the grove. Let me try to explain or I can send a fax. The second ring grove is top to bottom .126 of an inch and horizontally is .186 deep. The step on the bottom of the grove is .056 in from the face of the piston and is .100 from the top of the piston grove to the top of the step. The piston are marked a "M" Mahle never answered any on my questions. Do you know where I can purchase piston rings the car body is perfect

Answer
tough one Richard, sounds like the pistons were replaced, walls bored

I would start here with Rusty ,
http://www.buymbparts.com/

you can IM him from his home page
he has a lot of connections
you could also become a member here
http://www.peachparts.com/shopforum/index.php we are a bunch of MB nuts, some have specific information that I do not have, I am sure someone there could help you out

Let me know what you find out
Ron