Hypothetically speaking it is ILLEGAL to remove identification from a motor vehicle without permission. It therefore could be illegal to possess the id tags as they had to come from somewhere.Which could make the finished car subject of a fraud if it ever sold as the car did not come out of the factory with that id on it.

I scratch my head every time I see a body shell on ebay with no tags because the only reason you wouuld want the tags is to rebirth another vehicle.