Following comments on this list I bought one and eventually managed to fit it. It's designed for the bottom bracket to use the bolt holes for the right rear grab handle. Which is fine if you have a "normal" rear chassis cross member. Mine isn't, probably because it's a 50th Anniversary and has the NAS style rear step. Having discovered this I spent an afternoon driving round the car parks looking for Defenders and looking at the rear cross members. (Just checking the 'oles officer, really). Found 3 types, standard with all grab handle holes drilled, mine with none and tea break model with all holes drilled except the ones you want - the left hand pair on the right hand grab handle.
By installing top bracket first I was able to locate the centres of the holes for the bottom bracket and successfully drilled and fitted the hinges.
The rest of the installation was straight forward and the carrier works well. It's a nice bit of kit. However what really disappointed me was that having paid for the top of the range kit it was necessary to cannibalise bits off the old mounting kit to complete the job - only a few nuts and bolts but you would have thought they would supply a new set rather than you have to use rusty old parts.
So I now have going spare a rear door mounting kit minus half a dozen nuts and bolts, free to a good home if anyone wants it - I'm about 7 miles off J16 or 17 M6.