if you didn't start the engine in 2-1/2 yrs i would take all the spark plugs out first and squirt some diesel fuel into the cylinders and leave it to sit for couple of days - it would soften up any rust or deposits that dried out over time - then you spin it slowly by hand 10 turns or so, crank it with the spark plugs out so it won't start and clear out the diesel from the cylinders (also take out the fuel pump relay so there's no fuel coming in thru the injectors). once you did that replace the oil preferably with an oil meant for flushing/cleaning (i think you can still buy those) - you should actually do that before you crank it. i would then start it and let it idle quite a bit and then replace the oil again with one that you would run on a regular basis. o-rings can dry out but i would say that you'll probably be fine to start it like that and go from there (of course once you put the fuel pressure relay back in and set the contact on so it will build pressure look at the fuel rail side of the injectors to make sure they're not leaking). You should also check the brakes and power steering to make sure it's safe to move around (including the e-brake), take it for a quick spin around (really slow and not around pple - and be ready to use your e-brake), brake a few times and then recheck to insure there are no leaks (the rubber sometimes gets stuck on the metal and it breaks once you start pressing the pedal - same goes for the clutch).
EDIT: you should squirt some oil in the cylinders after you let it sit with the diesel in for couple of days and give it a few ours to penetrate -there could be some product out there to use instead of the diesel fuel and that is meant specifically for this but don't know of one, i always used diesel - if you do use something else make sure it has some lubrication features or add the oil in there before turning the engine, you don't want something that would wash out and dry or it could scratch the cyl walls.
