Stuff can fall into engines, especially in if they have been lying about in storage for a while. I would advise opening and checking everything you can in case that engine has been accidentally showered in wood screws at some point. Best to be safe!
I remember a Mate finding a manifold nut on top of a piston on a fresh built 5sgte.
It wasn't a pretty picture and cost the garage a small fortune to replace it
It was an engine I initially got to rebuild but has been serving as a doner...
The screw was just seemingly pushed into one of the ports. The engine had light scrapes on one cylinder I remember when it was running it would fire oil out the dumpvalve