Just look on the side of the block, if it's 4wd it will have 200 stamped, if 2wd it will have 205 stamped, if it really is a RS500 block which I doubt, it will have very small core plugs, and would be worth a lot of money to the purists.
What kind of boost you running ?, do you have any power printouts, these will give a clue about the engine + turbo spec.
I have a water pump to hand from a 2wd so can confirm if it is 2wd no problem.
tabetha