sounds a bit iffy,
he cant know exactly what damage has been done if aint had the head off,
if its done the valves as hes put it the block and pistons prob arnt gonna be great,
and like others have said if it is worth 10,000 like he says its worth why not spend 100quid on a head or 700 quid on a uprated one, also sounds like he wants top money for it.