To clarify all the questions asked:
1. These seats require NO modification to your rear tub. The factory Land Rover folding loadspace seats require you to CUT out a significant portion of your wheel wells, purchase or fabricate a new wheel well, and rivet or weld them into the cut. Not reversible on your "rare" NAS Defender. So to make the genuine LR seats work, you would need to purchase the tub inserts at minimum, which are not cheap, and require mods that most weekend warriors cannot/will not do. So you'd be paying for that as well. Finally, read around, but the seat belt mounting points are different on the TDCi and NAS trucks, with folks here on this forum (much more Roverish than I) stating that it would require major mods to get a secure attachment point. The Exmoors probably fall in a similar category, but from what Ive researched they are designed to bolt into our Defenders.
2. The only additional bit required for install of these seats are the rear upper seat belt mounting brackets. Everything else is a part of this kit including seat belts. About $80 for the pair.
3. Price: These are over $2400 a set from RN, plus the wait and shipping costs. Prices vary depending on trim material; these are near the top in terms of price as they are half leather/half cloth mesh centers with white stitching. Im selling for the what I have into them.
4. The only plus I see for the LR seats is that the genuine LR seats have a space between the seats when down and the Exmoors do not. I also think the LR seats look nicer.
Bottom Line, you'll end up paying just as much if not more to install the genuine rear loadspace seats, have to do a non-reversible modification to the body, and for many of us pay someone to mod the tub. Buy my Exmoors and bolt them in in your driveway!