There's some information and details about the 2-litre diesel on my website (http://members.lycos.co.uk/threelandrovers
) - go to the section called 'The Encyclopedia', then 'Engines'.
Basically, the 2.0 diesel was the first all-new engine used by Land Rover, being an Overhead Valve design instead of the Inlet Over Exhaust system of the earlier petrol units. The later 2.25/2.5 (petrol and diesel) engines and (I think) even the 200 Tdi engine were all based on this engine in some way- that's about 50 years of life.
The 2.0D develops 51 horsepower and 87-lb-ft torque- not a lot of either. It is a rather noisy engine and in a Series I Land Rover gives a top speed of about 45/50 mph.
Reliability is mixed- generally it is quite good, but at high mileages and if used at high speeds frequently the cylinder heads crack between the valves. The injector pipes are prone to splitting, reducing power and producing smoke. If the engine sounds very clattery and the tappets are correctly set, check that the pre-combustion chambers have not fallen out (as had just happened to my 2.25 diesel
)- this is expensive to fix.
They are rare engines and spares are very hard to get. A few parts can be taken from the 2.25 version, but really the only spares will come from owners clubs or any other 2.0D engines you can find- no major suppliers stock 2.0D parts.