Richie - I did this job on my old 2.5 a few years ago. Nothing too technical about it really. Mostly undoing and doing up bolts really.
I Had the front up on axle stands, undid everything that needed undoing (I dont think I took the cats off iirc) Had a trolley jack under the box to support it and then had a hell of a job manouvering it out to a position where I could lower it - then it fell off the jack onto my hand.

.....so when you get to the point where you are about ready to take the box off, it is by any sensible method, strongly advisable to have a second pair of hands. As said, its bloody heavy.
Same when putting it back in, try as I might I couldnt do it by myself - got a second pair of hands for about 20 minutes to help steady it and get it back onto the rear of the engine and get a couple of bolts started. After that you are ok on your own. Just a matter of bolting everything back in reverse order.