Here's my experience doing it on a 602 -
"I just put a new fan clutch in my 1992 300D 2.5 Turbo (has a OM602.962 engine). I followed the instructions at
http://www.peachparts.com/shopforum/showthread.php?t=158069
Those instructions are for a E300D, but basically they are the same and very helpful, with the following caveats and tips.
1. You don't need a special tool to lock the waterpump flywheel so you can tighten the fan bolt on. A small hex Allen key (is that what they're called in the US?) fits in the hole just fine.
2. There is a lot more space with the 300D than there is for the car in the instructions above, so a shortened 8mm socket is not needed.
3. I found it easiest to undo the 3 bolts holding the fan on the clutch and take the fan out. Lots more space to get in there. Not sure it helps massively overall, but if you're having trouble getting in there and getting it done, consider removing the fan, it's easy.
4. Get the 606 fan clutch - much cheaper than the 602 fan and is the same, as far as anybody can tell - fits straight onto the 602 and has the same engagement temperature. I got mine for less than $80 with delivery on ebay.
While you're in there, you may as well replace the serpentine belt. It's easy. The only thing that takes a little thinking is getting the belt tightening system figured out. What you do is undo the nut holding the spring on. Then use a lever to release the tension (there's a hold in the black plastic mount that allows you to do this easily) and take the spring off. Then it is easy to put the new belt on and put the spiring back. "