You could try replacing the prop shaft. My understanding is the car will run without a prop shaft, so that may well me all the previous owner has done, just removed the prop shaft. You need to check the transfer box is still in place and hasn't had any of the gears removed, as this is sometimes considered when people have transfer box issue. I recommend if your transfer box is ok then change the oil in it, it will help extend the life.
If the transfer box is in place you could try rotating the prop shaft connection. it shouldn't turn when the vehicle is stationary.
New prop shafts are hard to come by, I think its about £1500 for a new unit. The universal joints are also sealed for life so you need to check the condition of any second hand units. Theres a new one on Ebay at the moment for around £350, second hand units are approx half that piece. Do check the part numbers though to make sure they are compatible. You will need the bolts also, be careful here I think prop shaft bolts are hardened.
Hope that helps Richard