Philip Bosco, Ruben Santiago-Hudson and Jeremy Bobb are among the thesps joining Jim Norton, Cheyenne Jackson and Kate Baldwin in the upcoming Encores! production of “Finian’s Rainbow.”Bobb (“Is He Dead?”) will play the leprechaun who causes a ruckus when he chases an Irishman (Norton) to the American South. Bosco portrays a racist white senator who is turned black by the leprechaun’s magic. The Encores! semi-staged reading of 1947 tuner “Finian’s” — with music by Burton Lane, lyrics by E.Y. Harburg and book by Harburg and Fred Saidy — runs March 26-29. Warren Carlyle (“A Tale of Two Cities”) helms and choreographs.