) "Dwelling" means any building, structure, or portion thereof which is occupied as, or designed or intended for occupancy as, a residence by one or more families, and any vacant land... in section 804 of this title shall apply: (1) Upon enactment of this subchapter, to-- (A) dwellings owned or operated by the Federal Government; (B) dwellings provided in whole... has been made in full prior to April 11, 1968; (C) dwellings provided in whole or in part by loans insured, guaranteed, or otherwise secured by the credit of the Federal...