The big nut on the viscous coupling is 36mm A/F and despite what some of the manuals say it's a standard R.H. thread on the 4.0 and 4.6. Give it a few sharp taps to the left and it should spin free.
Remove the top fan cowl, remove the plastic fan as above, get a long breaker bar or similar with a socket fitted onto the belt tensioner pulley bolt and turn clockwise-you are pulling against a hefty spring, remove the belt. Now remove the bolts holding the water pump to the front of the block-these are different lengths so make a note of where they go. The water pump gasket probably will hold the pump in place-give it a couple of gentle taps to break the seal. Suggest after refitting that you fit a new belt for the sake of around a tenner. The viscous coupling is a bit of a pain to get the threads to start as they are a fine pitch and needs to be presented dead square to the threaded spigot on the pump, spin it on and give a sharp tap clockwise to the spanner just to nip it up, it will bed itself in when the engine is running.
Make sure you remove all traces of old gasket from the block before fitting the new one, A smear of Hylomar gasket sealant won't do any harm either.