From the exterior, the townhouse fits right in with the other quietly opulent residences on a leafy street on Manhattan's Upper East Side. Its floor plan is no less classic, consisting of "10 chunky rooms, all in the same proportion," according to designer Ann Pyne. In the library, paintings of peacocks and horses hang above a sofa upholstered in a Manuel Canovas silk velvet, with trim by Samuel & Sons; a pair of lamps by Tif- fany Studios, purchased from Rago, sits atop reproduction Chinese...