Sounds a bit pricy but then again it does sound like a good 'un... We paid about £1200 18 months ago for a 1994 M, 130k miles and similar condition (although did need a new radiator).
The LPG conversion probably took about 4 days in total (in our case spread over about 6 months!!!) The kit cost about £900, but we took it to a LPGA approved installer for safety checking - that's when the fun started. They had it for about 2 weeks, there were a couple of leaks so they had to replace a few olives and they had problems getting it to run well on LPG (which they blamed on the kit - I reckon it was more that they were unfamiliar with the kit as they didn't supply it). Having said all that I am still in favour of LPG as it runs well, slight loss of power but not much to worry about. Do you have good LPG availability where you live? Might sound an obvious question but we only have a 150-200 mile range with 2 36 litre tanks (usable capacity about 50 litres).

I would offer not more than around £1350 for it, be wary of plating on the floor, is anything more sinister being disguised here? Have you had a good look at the chassis for rust around the outriggers and the rear crossmember? Is there much rust under the bonnet, particularly the inner wings? Excessive rust around the brake servo area is an instant fail!
Has it got a full service history? 100,000 miles is nothing for a well maintained V8, but camshafts can wear prematurely if oil not changed when it should. You could inherit big bills, ANY doubts...... walk away.
And yes, the chunnel is out of bounds for LPG vehicles.

Well guys, after weighing up all the pro's and cons I've decided not to go for this particular Disco, just seemed too pricey (cost with fitting LPG would have been over £3500) for a car with no known service history.

Anyway we've just bought a cheap Mondeo yesterday as a "make do" car to replace the courtesy car while the search continues for another Disco. Thanks for all your help and advice, much appreciated.