When the sites, structures, and other properties authorized for acquisition under and endowment funds in the amount of $100,000 have been transferred to the United States, the Secretary of the Interior shall establish the Saint-Gaudens National Historical Park by publication of notice thereof in the Federal Register. Following such establishment the Secretary may acquire by donation, purchase with donated or appropriated funds, or exchange 279 acres of lands and buildings, or interests therein which he deems necessary for addition to the Saint-Gaudens National Historical Park and which, when acquired, shall become a part of the park.