Sally Struthers has lost a dramatic amount of weight, we’re told. The star, best known for playing Gloria Stivic on “All in the Family” in the ’70s, will be showing off her new silhouette as master of ceremonies at the Theatre Communications Group 50th Anniversary Gala tomorrow at Espace. A source tells us: “Sally has lost a lot of weight, and this is the first time she’s been back to New York since. She’s as tiny as when she appeared as the apple of Archie Bunker’s eye on ‘All in the Family.’ She looks fabulous.” We’re told the event will feature performances of musical numbers from three new shows, “Hands on a Hardbody,” “Giant” and “Super Fly.”