If the VIN stamped onto the block has been in a vehicle registered and previously licenced in BC (that would match the rest of the VINs for the vehicle), it should show up on the system. If the vehicle it came from was never registered in BC, then there will likely not be any records other than the import documents. If he doesn't have any of those, I'd be weary.
If there is nothing that comes up in searches, or with inquiries with ICBC and police, then you've done due diligence. HOWEVER, if at some point someone reports that engine being stolen and its eventually run by whoever and found to be stolen property, make sure you've documented your efforts and be prepared to hand over the engine as being stolen property.
"Never give a match up halfway through. Never say that you do not feel up to it, that your condition is bad, and throw in the towel. Fight to the very end, always looking for your chance to break through." - Kazuzo Kudo