An 86-unit apartment complex in Portland originally built as a hotel in the 1920s has been sold for $7.3 million. The Ambassador Apartments at 37 Casco St. is the latest in a string of multifamily housing structures that have changed hands in recent months, said Vince Ciampi, a broker at CBRE|The Boulos Co., who represented the sellers, Shirley Quirk and the estate of John J.