On March 20, the Zoning Board of Appeals is scheduled to hold a hearing on plans to redevelop the downtown armory building at 76 Court St. Constructed in 1906, the medieval-style brick fortress was used by the National Guard and once housed the Plymouth Juvenile Court. In October 2010, it was auctioned off by the state and purchased by Plymouth Armory LLC for $418,000. Now Megryco Inc., a property management company, is seeking a special permit to convert the armory into apartments and commercial space. The hearing is scheduled to start at 7:30 p.m. in the Mayflower Room at Plymouth Town Hall.