Just fitted one to a 200 Disco.
It's really not a difficult job to do:
Crawl under the car taking a ratchet with a 19mm socket with you
Find the PTO cover (It's between the hand brake drum and the exhaust pipe, but above both by the way)
Undo all six bolts on the PTO cover
Discover that your transferbox has been overfilled and get an armful of Dexron transmission fluid
Scrape out the brown gunge at the bottom of the PTO cover and in the centre of the main gear (not actually very much of this on mine)
Do the wear check - chock the front wheels, jack the offside rear, put the car in 4th (1:1 gearing) and release the handbrake - now crawl back under the car and wiggle the handbrake drum and see if there's any slack between what's happening at the propshaft and the maingear - there wasn't in mine, however there was around 1/4 turn of windup available through the gearbox as a whole)
Mark the state of the mainshaft on the little sticker on the back of the splasher plate.
Piss around for 5 minutes before realising that gaskets are 3 dimensional things and have two sides.
Get the gaskets aligned with the holes in the PTO cover and the splasher plate
Stick a couple of bolts through to hold everything in place (I used the ones at 11 and 5 o'clock) and offer the cover and splasher up to the back of the PTO housing
Spent the next half hour cursing as you batter your knuckles off the handbrake drum/exhaust/underside of the car as you try and use a ratchet to do up 2" long fine grained bolts.
Damage your knuckles seriously trying to nip up the bolts and having the ratchet fall off the heads.
Take the car for a drive and wonder at the sudden lack of Whizz sounds coming from the transfer box.
The kit actually comes with a damn good set of instructions with an extremely good diagram. Not bad value for £23.50 shipped.
P.