I've been looking for a Honda F20 engine and one has come up but just before I shell out the asking amount I had a thought that what I'm buying could be stolen, or more to the point can I prove it hasn't been ?

How is the best way of going around checking these things ? obviously if the engine numbers were ground off it then I'd walk away but if their not then how can you prove its all legit.

Any help would be appreciated as a stolen engine isn't going to be much use in a road car