I replaced the water pump in my '88 260e so it is fresh in my mind and this info may help:

- no need to remove radiator at all, period.
True


- the fan shroud needs to be losened by removing the two clips only, leave the shroud in place, removing the clips allow you to move the shroud over a tad so that ...
If you have a one-piece fan shoud you need to loosen the clips and move the fan shroud to access the 8mm allen socket in the center of the fan clutch. There is a special tool that can be made to hold the fan pully while you loosen the bolt. It is usually pretty tight. You need to remove the fan clutch, fan shroud, and fan pulley.

- you can losen the 14mm tensioner bolt just below the long adjusting nut
First you need to loosen the 19mm nut on the front of the tensioner 2 turns. Then loosen the 13mm adjusting rod at the top of the tensioner CCW until the rod is flush with the top of the nut. This should allow you to remove the serp. belt. You may have to pull on the belt to compress the shock before the belt will slip off.


- remove the airfilter housing (2 screws and losen the vertical one on the side to give more working room (not critical but easy to do and less frustration)
Definitely remove the air filter housing. There are 4 - 10mm screws on top that need to come off also.

- unbolt the dipstick fastner near the top so that the dipstick can be moved a little to get better access to the 2 rear 13mm bolts hoding the waterpump (again, not critical but easy to do and helps to get access)
The dipstick fastener is easy to remove and will allow access to the upper rear bolt on the water pump. I was able to loosen the bolt with a 13mm box wrench and a 13mm open end wrench from above. A 12 point wrench requires 30 degrees of movement to get a second bite and there is not 30 degrees of clearance. That is why you might need a couple different wrenches with various offsets. I used a 3/8" u-joint to remove the bolt after loosening it from above.


- remove the front 6mm Allen bolt with an allen tool and a bit of pipe to get more leverage.
That is exactly how I did it.

- the lower rear 13mm bolt comes out easy with a 3/8 drive and extension
I used a 13mm socket with a 12" "jiggle" extension that bends slightly but is more stable than a u-joint. It worked real well for me on this bolt.

- the upper rear 13mm bolt I found a lot trickier because of not very much room, but finally found that a combination of the smaller 1/4" drive to the bolt and then a 3/8" extension did the trick perfectly.
The upper rear is the most difficult but by working from above and behind you can get it.

- Now, my big question ..... how the hell do I get at the front lower bolt do I need to remove the tensioner mechanism and the cylindrical reservoir next to it (dont know what it is ... maybe power steering?) Please say I don't need to do this ... is this where the dealership earns their 5 hrs charge
The lower front bolt is easily accessible with a 13mm wrench after the tensioner is removed. The tensioner has to be removed to physically remove the water pump from under the manifold. The two PS pump bolts attached to the tensioner mounting plate also need to be removed to allow the pump to come out. I tried getting the pump out without moving the PS pump and could not do it. Removing the PS bolts is not difficult though.

One thing not mentioned is that the fan, PS pump, and Water pump pulleys all need to be removed in order to remove the tensioner. I sprayed PB blaster on the bolts and shafts first to loosen them up. To keep the pulley from turning while loosening the bolts, I used an old serp belt wrapped around the pulley and under the crankshaft and looped over the alternator pulley. The pulleys are usually tight on the shafts. Mark thier positions relative to the shaft and be carful not to distort them when removing. I tapped them off using a long screwdriver and hammer. Tap them as close to the hub as possible. The left bolt on the tensioner needs a dab of RTV sealant when replacing because it is treaded into an oil passage.

It's not a difficult job if you have patience and allow yourself plenty of time. I have found that working on a Mercedes is 90% mental and 10% hands-on. It sounds like you are already sorting through the mental part.