Never did a gas engine, but on a W123 Diesel you have to remove the fan, and once you do that the rest is pretty straight forward.
I have heard people suggest they take the radiator out, but I have never done that. I end up with some extra skin scraped off my fingers and hands but managed to do the job without the hassle of taking the radiator out. I did this once in a parking lot after noticing a puddle of coolant under the car when I came back from shopping. Left the family in the McDonalds, found a water pump at a local parts store, and went back to McDonalds and did the job with the kids and wife watching from the window.
I believe there are 4 bolts that hold the fan on, and once it is off, getting a wrench into the area to remove the pump is not the same challenge it is with the fan on. Couple hours the first time you do it, if you have the parts in hand.
Good luck and I hope this helps. Jim
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)