An individual, business, or NFA Firearms trust may not register an unregistered NFA firearm. Only a manufacture, maker, and importer can register a firearm.
Possession of an unregistered NFA firearms is a crime. The ATF states that if you are in possession of a contraband firearm, you should contact the nearest ATF office to arrange for its disposition.
WARNING – although this is the advise of the AFT, they also state that mere possession is unlawful