I have run 2 fans on my v8 now for about 6 months.
I bought the slimline ones off eBay, bout 50 quid each. I'm on my second set, the first ones were 25 quid each and didn't last.
Anyway, I got a fan switch for an aircon disco and fitted it to the oem position in the thermostat cover.
V8 disco, look at your thermostat housing top and you'll see a flat bit on the tube.
Drill this out and tap it m22x1.5 iirc and fit your oem fan switch in there.
They're about 15 quid from intermotor so cheaper than x-eng kit and a neater install.
Switch on the dash and she wades without drama.
Cheers