Depends on what you are going to use it for. If you want to go rallying, keep it original. If you want to drive it, make a few subtle mods to improve liveability. Maybe power steering and better seats, things like that. I would try and keep it so you can put it back the way it was if you want to sell it, original usually makes more with old vehicles.
Quite a lot of work in a camper conversion, and that will really ruin any collectors value. If you want/need a camper, it might be cheaper and easier to buy one.
Sure they did, maybe tens of thousands.
But having seen the way squaddies tend to "look after" a vehicle, it is possible not all that many are in good condition now!