Start the Fans please, help required

Hey folks, getting busy with the spanners this weekend, MOT is due next month and the to do list has been slowly growing. So hope some ideas from you guys will guide me forward on one little issue. So I'm replacing my old knackered Radiator amongst many other things, I'm going to fit up switchable elec fans once done and therefore want to remove the old engine mounted fan, the quick amoungst you will see from the picture that whilst it is a 90 the motor is a Nissan lump, the question is this how do you rekon i go about getting the fan off? there is no fixings/bolt heads on the outside. the only fitting was a coiled spring which i have taken off from the very centre, there is nothing down the back like spanner on the shaft etc. and i'm just short of brut force for answer at the moment.
Any clues????
[/IMG]

undo those bolts around the edge of the visco clutch. then move the fan toward the engine and get in between with a big adjustable spanner. think its 30 or 32mm. you may have to hold a screwdriver between the nuts on the pulley to stop that turning as well.