The 36-story luxury residential rental at 800 Sixth Ave. between West 27th and 28th streets is in contract to Greystar for $240 million. Developed in 2003 by the Adell family’s Adelco, which had rezoned the old Flower District, the Archstone Chelsea has 266 apartments of which 62 are still rent-stabilized, a roof-deck, a fitness center...