FORT WAYNE, Ind.—City developers are betting they can turn an abandoned complex, where General Electric Co. once employed almost 40% of the city’s workforce, into a development with loft apartments, an incubator office space for startups and a food hall.

The goal is to transform the city of 260,000, which has seen stagnant wages, a decline in domestic population and hasn’t fully been able to replace thousands of manufacturing jobs lost in the 1980s.

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