The upcoming revival of Tony Kushner’s “Angels in America” at Off Broadway’s Signature Theater has begun to firm up its sked, with the production now set to begin perfs Sept. 14.Show, helmed by Michael Greif (“Rent,” “Next to Normal”), will open in late October with an exact date to be confirmed. Two-parter “Angels,” which nabbed back-to-back play Tonys in 1993 and 1994, is one of three planned offerings for the Signature’s 2010-11 season, which will be entirely devoted to Kushner’s work. Remaining two shows have not yet been nailed down. Angels” will be the second marathon-style outing from Signature in two seasons. The org currently presenting a multi-month run of Horton Foote’s three-part epic “The Orphans Home Cycle.” No cast for “Angels” has yet been set.