One of New England's premiere developers wants to convert the long-abandoned mill at 34 Franklin St. into 166-175 apartments and place it on the National Historic Register to preserve the history and character of the Millyard site overlooking the Nashua River, city records show. Brady Sullivan Properties Inc. of Manchester bought the 310,000-square-foot building and adjacent boiler house once owned by the former Nashua Corp. on Aug. 14. The sale was handled by Lofts 34 LLC, a Brady Sullivan holding company.