If it's a plane Jane Camaro then I don't see anything wrong with explaining that the tag was missing (that's if you even sell it) and you put a replacement on it so as to keep it looking the way it did.
If it doesn't have the codes for the more in demand models then its obvious you aren't trying anything suspicious. But for a plane Jane, who cares.
Look out on eBay for one that fits your period this way you likely will get a real one and the chances of a reproduction being recognized will be a moot point, but be forwarned that those tags are tracked and recorded in a DB at CRG
Good luck with your restoration,