Just saw this message today. I don't have your chassis, but I have done this swap on both of my cars, 123 and 124, and they are basically identical, so I assume yours is similarly built. You have to get your console panel out, which I am unfamiliar with.
Once you can see where the shifter goes, the shaft is threaded at the bottom, with a lock nut. Move the shifter to the middle of the range (D, 2) to make it easier. Hold the shift knob tight and undo the lock nut (15 mm). Unscrew the knob. Depending, you probably have to remove the locknut completely to remove the knob from the shift guide, and replace with new one.
Getting the knob to sit straight is the hardest part.
1985 300TD 4-speed 212K
1992 400E 343K
2001 E320 72K