With their magisterial wigs, frilly shirts, made-up names and three-farthing British accents, Boston’s Upper Crust evokes a long-gone era-namely, the ’60s, when gimmick bands were as common as Sheep. Groups that dress up and write topical theme songs usually do so because they can’t get anywhere on their music, and that would certainly seem to be the case with the five indolent artistocats of the Upper Crust, formerly a New England surf band called the Clamdiggers with roots in such credible combos as the Lyres, Bags and Titanics. The half-hour-long Let Them Eat Rock quotes liberally from AC/DC (“Let Them Eat Rock,” “Little Lord Fauntleroy”), the Troggs (“RSVP,” “Who’s Who of Love”), Sex Pistols (“Minuet”) and Vapors (“Little Rickshaw Boy”), adding nothing but Mad-level parody lyrics to the rote garage-rock. Off with their heads.