I just did a google to see if I could find an image of a Disco and a Defender 200tdi and I couldn't - I found this though:
200TDi engines come in three flavours, identified by the engine number which starts 11L, 12L or 13L.
11L - this is the version used in Defenders from 1990. High-mounted turbo, low-mounted injection pump. If you are offered one of these at a sensible price, complete with all ancillaries, snap it up. The conversion becomes a straight bolt-in swap that you can probably do in a day. Be aware however that the manifolds are no longer available new and almost impossible to find second-hand. To be worth having a Defender 200TDi has to have the manifolds, power steering bracket and pump, radiator/intercooler assembly and pipework, air cleaner with bracket and hoses, oil cooler pipes and fuel filter housing. Some of these parts are still available new but not all, and they will be very hard to find second-hand.
Defender 200TDi '11L' engine - note high-mounted turbo. Do not confuse this with the old '19J' turbodiesel which also has a high-mounted turbo. TDi has a nearly flat, ribbed rocker cover, 19J is rounded and smooth. I know someone who paid a lot of money for what he was assured was a Defender TDi engine. What turned up on a pallet was a knackered 19J. He was not happy and I don't think he managed to get his money back.
12L - Discovery with manual gearbox. This is the most common variant and the one with which these notes are mainly concerned. Only one significant design change around the end of 1992 where the design of the unions on the oil cooler pipes was altered. (See 'Oil cooler pipes' later in the article).
13L - Discovery with automatic gearbox. This is the same as the 12L except for the backplate and flywheel. If you are replacing a very late 2.5NA or 2.5TD you can use the flywheel housing and flywheel from your old engine, otherwise you will have to try and track down a dead 12L to provide the parts.
In 1993 Land Rover replaced the 200TDi with the 300TDi in both Defender and Discovery. This is a different engine in many respects and not what you want (I will publish a guide on installing the 300TDi when I get round to it). Main identifiers are the engine number (300TDi start 16L or 23L) and the belts at the front. 200 has two Vee belts, 300 has a single flat ribbed belt and spring loaded tensioner. On a 300 the air intake on the turbo faces towards the rear of the engine, on the 200 it faces to the front. That should be enough to stop you buying the wrong engine by mistake.