The Secretary of the Interior is authorized to have competent and disinterested appraisals made as to the value of not more than twenty-three acres of land in Gettysburg National Military Park, in the State of Pennsylvania, such land lying generally between East Confederate Avenue and Wainwright Avenue, and being situated adjacent to the present high-school property in that area. Upon the basis of such appraisals, the Secretary is authorized to convey such property for public-school purposes to the State of Pennsylvania, or the appropriate local agency thereof, the conveyance to be made in exchange for non-Federal land of approximately equal value, which land, upon acceptance by the United States, shall become a part of Gettysburg National Military Park.