The trustee or trustees to whom a patent has been issued for a townsite surveyed pursuant to section 732 or 735  of this title, upon a finding by the Secretary of the Interior or his authorized representative that any Alaska native who claims and occupies a tract of land within such townsite is competent to manage his own affairs and has petitioned the Secretary or his authorized representative for an unrestricted deed, or  shall issue to such native an unrestricted deed, and thereafter all restrictions as to sale, encumbrance, or taxation of said lands shall be removed, but said land shall not be liable to the satisfaction of any debt, except obligations owed the Federal Government, contracted prior to the issuing of such deed.12