You can use a large adjustable spanner for the nut but you need something to stop the waterpump from spinning like the tool in the previous post. I would try to fit without removing the fan as its possible
See the vid for P38 which should be very similar
[ame=http://www.youtube.com/watch?v=EG1x6JZJ1cE]Range Rover - How To Replace Water Pump P1 - YouTube[/ame]

