Michael,
You are so right, the rubber donuts go first. I did get my system on, by a Austrian mechanic living here in the Williamsburg area, that has had years experience with W113s and 111s. I help in the process of placing the parts on, we had to take off system several times in order to get the pieces to fit perfectly, then to spot weld system. We then had to take the system off again to complete the welding. This became a 1 and a half day experience. Problem is that a MB welded system has no extra mm of length on the pipes to play with unlike a clamped system. Hindsight maybe a SS clamped system would have been better and a lot quicker to put on.
Bob