Hi,
I put a 200tdi in a disco 2, that had a 3.9 V8 in it, although mine had a manuall R380 box in it I still needed a shorter bell housing and to change the spigot bearing to make it fit, but to find that out I rang David Ashcroft at ashcroft transmissions, quoting him the engine and gearbox serial numbers and he was able to tell me what i needed and surply them at a very reasonable price,
There are one or two little snags you will come across, but it is a more than do able conversion, hope it goes well