The 540,000 sq. ft. 25 Broad St. will be converted to residential use by Crescent Heights and is expected to be the first conversion project to come online downtown. Rockrose Development Corp. also is planning to convert the entire 500,000 sq. ft. at 127 John St. to apartments, says John West, director of planning at Rockrose. Construction activity is expected to begin later this year with completion in 1997.