It's only the 5th gear which is different on the Diesel box, the rest are the same. Not sure if you can still get them but you used to be able to buy the Diesel 5th gear for the mainshaft and a complete Diesel layshaft from Ford. It is possible to press the 5th gear wheel off the layshaft and replace it with the Diesel one but by all accounts you need a pretty beefy press to do it.

I got T boned in my XR4x4 back in 2010, the nearside rear wheel ended up with a funny toe in angle. Looking underneath, you couldn't see anything bent apart from the ARB drop link on that side. For complete peace of mind, I replaced both semi-trailling arms, the beam, diff mount and drop links. It's fine now.