Thanks for your input Tazza.
Diesel will leave slight amounts of oil in the cylinders, but remember when it was running it burns almost all the fuel, so there really isn't a nice coat on the cylinder walls to protect it. If moisture got in, it can rust a little.
If it was me, i'd pull the head too. With the head off, you can use oil/atf, remove the con rod bolts and knock the pistons out if there is no obvious rust in the cylinders.
Another way is to remove the injectors and try and get a bore camera, if you can get one into the cylinders, you can look for obvious rust.
Just how hard have you tried turnng the engine over? Ensure the engine is not being locked up due to the hydraulics/hydrostatics holding it.