No railroad in reorganization in the region and no person leased, operated or controlled by such a railroad shall sell, transfer, encumber, or otherwise dispose of rail property, or any right or interest therein, designated for transfer to the Corporation or conveyance to a profitable railroad in the final system plan, except pursuant to section
743
(b) of this title. The provisions of this subsection shall not apply to any such sale, transfer, encumbrance, or other disposition—