Seems you got all the parts you need in one place so should be easy enough, provided you got all the tooling and man power requirements sorted out (those are the heavy bits of the car you will be moving around and you'll need all the help you can find). Provided your donor vehicle's 300tdi is one with the manual injector pump instead of one of the later engines with electronic controls, it should be a straight swap. Other than that, you'd be better off changing the transmission adapter plate on your 200tdi and mating the autobox to it instead of going the hussle of moving all the electrics to your defender. You are going to have to blank off the gear selector hole that is going to be left in the defender's center console after you take out the manual transmission. The auto's selector lever would then be riveted/attached to that blanking plate. Why the need to change anyway, a handicap maybe??