That's simple! The nut is some sort of torx that I'll have to hunt for, but shouldn't be too bad.
I don't need to remove the fan shroud, as I can nearly get myself between the engine and the rad, there's so much room. One of the benefits of these four banger cars.
The manual has a belt routing diagram, but I'll probably take some pics just to make sure.
1998 C230 "Black Betty"