you would want the V6 from a Taureg TDI to get enough power. And you'ld need all of the electrical system(s) to go with it. You wold be probably be fabricating a new exhaust, etc.
My 2.0L Jetta TDI has about the same amount of torque as my 4.0L ZJ had, but about 35% less HP. The Taureg V6 TDI has about the same torque/HP as my WK CRD V6, which is a bit heavier than the ZJ. Plenty of power in there
Now if you really want a good diesel engine in your Jeep, get an OM642! (std in the WK CRD)