If its got this far in life then the nikasil bore liners will be fine. If it hasn't had already, you'll need to replace all the timing chains and Tensioners. The plastic Tensioners break eventually taking the engine with it. The new mark vi Tensioners are metal and work fine. Budget about 1k for the work. If the gear box hasn't had the oil changed it will need doing, budget abut £500. As for the rust its common over the rear sills and arches. What you see is where its at, with that rust, it will need chopping out and filling. Most likely the bumper mounts will have started to corrode as well. Also check under the car, the foot wells can suffer as well. And the old exhaust and cats rust, They are solid and fairly reliable cars. There are 2 types of xk's cheap ones and expensive ones. Expensive ones tend to need nothing doing so cost very little to run. Cheap ones tend to need money spending on them, usually bringing the final bill to the same as an expensive