When the musical Jersey Boys opened on Broadway nearly a decade ago, it turned the story of Frankie Valli and the Four Seasons into Tony-winning musical-theater gold — which isn’t all that surprising, considering the show drew from the Four Seasons’ already proven catalog of music. For the play’s movie adaptation, Clint Eastwood directs a cast of stage vets — relative Hollywood newcomers — led by John Lloyd Young, with the exception of Christopher Walken as mobster Angelo ‘Gyp’ DeCarlo.