Superintendent Named: Michael S. Miller, assistant superintendent of curriculum and instruction, has been named superintendent of the Los Alamitos Unified School District, effective July 1, 1986. He will succeed Charles McCully, who has said he is resigning at the end of the school year to pursue "other options within education, as well as the private sector." The district's school board voted unanimously for Miller's appointment last week. Miller, 41, has been assistant superintendent since 1980. District officials said they have not yet decided Miller's salary. McCully was paid $68,000 a year.