I am the Trustee of an estate which contains a large firearms collection. My deceased uncle was a licensed dealer (FFL 01), gunsmith, and collector. Two of the items in the collection are identical Austrian WWII vintage sub-machines. The first one has a destroyed/cut-up receiver but appears to be good for parts (no paperwork specifically for this one). The second one has an intact receiver but has the barrel welded up. The second one has a letter (from ATF? - I don't have it in front of me) dated from the 60's (1963?) showing that my uncle was legally allowed to own it (is this a CLEO letter?). Assuming the state I live in allows private ownership of these firearms would I be able to transfer registration on a federal level? If so would it be possible (legally) to make one operational by combining parts from each? Any help/information on this is greatly appreciated.