The hard part with any airplane that someone has removed all numbers from is being able to say this is the airplane you are talking about. When one removes all data tags and such there is no way to say this number went on this airframe.
But if the person in fact did not remove the numbers but covered them then you could be in luck for now its just a matter of jumping through some hoops and doing extra paper work to get everything back in order. It can be done if in fact the numbers are still in place.