As if anything with “Orson Welles” in the title weren’t already rarified enough, this light and bright adaptation of Robert Kaplow’s historical novel, by screenwriters Holly Gent Palmo and Vince Palmo for director Richard Linklater, actually is pitched more for theater geeks than for movie geeks. But somehow, from the tale of a wannabe thespian bluffing his way into Welles’ landmark 1937 staging of Julius Caesar, the de facto slacker spokesperson Linklater has educed a universally compelling psychology of megalomania. His trick is to fold an avid study of play-making within the ostensible trifle of a golden-hued Zac Efron vehicle. And before you choke on laughter, consider Linklater’s longstanding knack for casting, which culminates here with a magnificently satisfying turn from Christian McKay as the best Welles (besides the original) that movies might ever give us. Next to him, Efron’s twinkling cipher seems like just what’s needed. And Claire Danes, in a fulcrum role, sparkles too.