IN THE MID-1950S, Savannah, Ga., was crumbling. The effects of the Depression had left the city’s buildings in disrepair. And as residents fled to new postwar suburbs, developers began planning to bulldoze many of the deteriorating, expensive-to-maintain grand antebellum homes, as well as the once elegant public squares conceptualized, beginning in 1733, by the city’s founder, James Oglethorpe. The impending loss radicalized many of the locals, among them an energetic real estate agent, developer and contractor named David Morrison and his wife, Zelda, who became part of a preservation movement that would lay the foundation for what the 2.2-square-mile landmark district would become: a mannerly grid of graciously restored homes,…