Andy,
Sorry to see that nobody replied to you, as I know there are members here who have replaced water pumps, myself not included.
What I can tell you is that the hood does come off. You need to take special precaution with the spring rod that supports the hood when open. Use an S-hook to hold it up to the hood. I've not removed a hood, but I believe I recall reading that you should mark the position of the hinges as it's very difficult to get the hood aligned properly when reassembling. Also, there may be spacer washers in the hinges, locate them before removal so you can reassemble properly. These hoods were hand fit to each car.
If the car is on a lift, the radiator can be removed and dropped out the bottom of the engine bay. Otherwise, with the hood off, you can lift it out the top.
I would think the job would be easier from underneath with a lift because the hood is difficult to remove/replace.
I'm suprised that SLS can't determine exactly what part you need if you provide your chassis number and engine number. Contact Tom Hanson (great parts guy at California, USA MB dealer) at halfviking@yahoo.com and provide your numbers to him. He can provide the precise part number. I've never received a wrong part from Tom.
Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both tops
1994 E420
