westonian,

There is a wealth of knowledge on this forum. If you search the archives you will find a lot of information about the 124 body style and wheel/tire size combinations that work without problems.

If you are looking for someone to pat you on the back and tell you that trying to make your set up work is a brilliant idea, you likely won't find that here. You then slam The Tire Rack which really isn't the way to win points on this site. Luke at The Tire Rack knows what combos will work with various Mercedes models and his advice should be heeded if you want a problem free fitment. If you think the manager at Les Schwab is such a guru, maybe you need to just turn the problem completely over to him.