In addition to the properties described in section
410z of this title, the Secretary shall study the properties described in this section to determine the feasibility and suitability of including them within the Boston National Historical Park. In making such studies, he may enter into tentative agreements with any owners thereof for their inclusion in said park and he may enter into options, for a nominal consideration, for the purchase of such properties, but no additional properties may be added to the park except by an act of the Congress. Studies shall be made of the following properties: