This article shall be applicable to only those redevelopment projects of the City of Richmond for which a final redevelopment plan was adopted by ordinance on or before July 1, 1975, and amendments thereto adopted on or before June 1, 1980. This article shall be applicable to only those redevelopment projects of the City of Pittsburg for which a final redevelopment plan was adopted by ordinance on or before June 1, 1980, and amendments thereto adopted on or before June 1, 1980. The Legislature finds and declares that conditions unique to the financing of redevelopment in the City of Richmond and the City of Pittsburg require the granting of authority to merge project areas.