I've just done some on a Discovery 2, not the same I know but there is a pipe that goes in to the top of the gearbox. To get it started I used a 19mm crows foot wrench on a 3/8" socket wrench to crack the nut, then once it was loosened I also used a shortened ring spanner with a section cut out. It was quite tedious since you can only just get you arm between the exhaust and chassis or between the exhaust and gearbox and then I could only move the spanner for about 1/8 turn but it is doable. The whole time you can never quite see what you are doing it was mostly done by touch.
Just make sure when you pull the pipe out you get the o-ring as well.