A substantial part of the housing in a housing project is deemed to be for persons of eligible income if: after financing is provided by the Montgomery Commission, 50% or more of the housing units are occupied first by persons of eligible income; 20% or more of the housing units are for low-income persons who are assisted or who are eligible to be assisted with federal subsidies; or the owners of the housing certify to the Montgomery Commission that they will make their best efforts to meet the standard under item (1) or (2) of this section.