Isn't the prop shaft the same as the W124?

I don't think you need to do all of that work.
First take off small transmission crossmember that holds trans mount. Then unbolt the coupling from transmission and from shaft, 6 bolts total (some are allen 8mm, and some hex). Then you just slide the shaft back a few centimeters.
You should have enough room to remove old coupling and insert new one. Slide the shaft back into place. They get stuck sometimes use a rubber hammer or longer bolts just to get it in place. Insert new bolts that come with the coupling. Put back the crossmember and you are done.

I've done many 124s. I apologize if the 201s aren't the same. It just doesn't make sense to me that the shafts are a different design and that you have to go through all of that work with the exhaust and center bearing.

Vin