A new play by Dustin Lance Black, about a trial to overturn California's voter-approved ban on gay marriage, has found its first cast members for a one-time staged reading on Broadway. Morgan Freeman and Anthony Edwards will be among the actors performing in "8," written by Mr. Black, the Academy Award-winning screenwriter of "Milk," and adapted from reporting and trial transcripts from the case of Perry v. Schwarzenegger, in which a federal judge in San Francisco struck down California's Proposition 8 in 2010. (The ruling is currently being appealed.)