Prior to the Gun Control Act of 1968, dewat machine guns were unregulated, no paperwork. If I remember correctly, the only requirement was that the dealer selling a dewat was required to record information on the original purchaser. The problem with dewats was that dewats were easily restored to full auto, eventually requiring registration in the GCA. This is an article, from the December 1955 American Rifleman, on the Internal Revenue Service's deactivation program.