2.5TD J19 grey/black smoke

I bought a 89 2.5TD some years ago, it sat in my drive but now i need to get it going.

The problem with it is if you rev it or drive it, it blows out black/grey smoke. Ive checked the turbo etc, but nothing stands out. I know there have a problem of burning out pistons. But i pray to the Land Rover gods I don't have to take out the engine and rebuild.

If it is a rebuild any ideas of a costs?

Crap/old fuel?
Injector pump timing?
Cambelt still okay?
Rubber fuel pipes leaking, allowing air in?
Got access to one of them laser temperature pointers? if so see if all exhaust temperatures are at the same temperature, as could be a sticky injector not contributing or over fuelling/hosing.

A compression/leakdown test would give you a reasonable indication as to the health of the engine. Fuel injectors can also coke up and lead to bad mixing, hence the smoke from unburnt fuel. My Discovery had sat for some time with little running and was also very smokey. A bottle of injector cleaner in a fresh tank of fuel, plus some motorway runs, helped to clear it up if they aren't too far gone.