Don't restrict yourself to just 200 Tdi. Its the same transfer box on 300's and the early Td5 ones although you need to make sure the difflock mechanism is still in the box on the Td5 ones (easy enough to do with the serial number or the fact it will have a "nipple" on the top of the box)
Gives you more choices. Make sure you get from a Discovery as the defender one is lower geared in high ratio