The Federal Reserve Board approved Charlotte, N.C.-based NationsBank Corp.'s $1.2-billion acquisition of San Francisco-based Montgomery Securities. . . . Dart Group Corp. is trying to sell its 52% stake in Crown Books Corp., a discount bookstore chain, to Wallace's Bookstores Inc. for $27.7 million, or $10 a share, according to Larry Schafran, a Dart Group director.