It’s Sunday night, and the Jefferson Orleans is buzzing as veteran orchestrator Pat Barberot’s big band kicks into a sizzling rendition of “Sing, Sing, Sing.” Decked to the nines, septuagenarians and octogenarians hit the dance floor, all of them relishing this wartime era wonderland. Not even the aftermath of Katrina can hamper the spirits of the club’s clientele, who remain determined to use the best of the past to enjoy the present.