Disbursements from the General Post Fund shall be made on orders by and within the discretion of the Secretary and in the manner prescribed in section 8523 of this title; except that (1) if the testator or donor has directed or shall direct that the devise, bequest, or gift be devoted to a particular use authorized by this chapter, the same, less expenses incurred, or the net proceeds thereof, shall be used or disbursed as directed, except that a precatory direction shall be fulfilled only insofar as may be proper or practicable; and (2) if the testator or donor shall have indicated the desire that the devise, bequest, or gift shall be for the benefit of persons in hospitals or homes, or other institutions operated by the United States but under the jurisdiction of an official other than the Secretary, the same, less expenses incurred, or the net proceeds thereof which may come into possession of the Secretary, shall be disbursed by transfer to the governing authorities of such institution, or otherwise, in such manner as the Secretary may determine, for the benefit of the persons in the institution indicated by the testator or donor, for proper purposes, as nearly as practicable in conformity with such desire of the testator or donor.