The MD kit is the only way to go.
Anything else would be insane. There is a specific kit for the Disco. Wiring, rad, mounts etc etc.
I've got an '04 Disco G4 and am about to embark on that journey, along with a 5 speed tranny. The way I figure, this thing will now last for a long time, and WAY better mileage (about 36 on the hwy). I'll be keeping this truck for 10+ years, so it will pay it's self off.