Its very doable. 4th is the same in the auto trans. put it in 5th and its got legs. Don't expect a smooth, precision shifter. It wasn't built to speed shift, just get you through the gears up to Autobahn speeds. There is no custom work or fabrication, only intelligent grunt work involving remove and replace. Best way to do it is to have the complete 5 spd donor car parked outside. Many (but not all parts) are the same between the W201 and W124 chassis. The "not all" includes the trans crossmember, an exhaust bracket, maybe the driveshaft (or front section of it). Do a search, much information available. Again, the best way do it is to have the complete 5 spd donor car.

__________________
Hanno
'79 6.9 Sold (after 27 years)
'83 280SL, 5 spd.
'94 E320 Sdn. 5 spd conversion
'02 E320 Sdn.(on loan to mom!)
'87 300E (5 spd. conversion) Sold
'05 E500 Wagon