Nice find! A JP3, as already mentioned, these are expensive engines on this side of the world - JP3s are much prized by canal boat owners as main propulsion engines. Plus they have that unique 3-cylinder off-beat tone, which seems to make them even more popular.
Used parts are readily available over here, I'm not sure what availability is in Australia (which, I'm guessing from your username, is where you're based).
Good luck! Some video of it running would be cool, once you get to that stage.