Knowing how much these cars rot (as I have one myself) this will need a very close look at.
Rust where the rear bumper meets the valance will mean the valance will be shot, body kit will more than likely have been fitted for a reason ie sills rotted. Floors will more than likely be rotten also jacking points.
If you wanted to get it back to original spec you'd need to find the gold dust rubber bumpers. Car has been resprayed without covering the stone guards so indicates a quick once over job, inner and outer rear arches will need a lot of work.
Interior has been / is very damp (steering wheel mould / keys rusty)
Looks like a younger owner with it having a body kit and blacked rear lights.
Anything can be sorted though (at a price)
BUT if I didn't have my XJS or it was nearly finished - i'd go for it as at the moment it's well worth it if you can sort it yourself