Plans to return this forlorn home to its Gilded Age glory were designed by a descendant of the original architect. A rundown rental at 471 West End Ave. in Manhattan is on sale for $6.95 million, but this vacant building comes with a grandiose redesign plan — and an architectural legacy to match. The 25-foot-wide townhouse was originally designed as a single-family townhome by influential New York architect Stanford White’s firm, McKim, Mead & White, in the late 1880s. The once-grand mansion spent the past several decades on the decline as a multifamily rental, standing as a strange holdout among...