Within three months of the approval of this article by the Governor, the governing body of any Class 2, 3, 4, 5, 6, 7 or 8 municipality in the State of Alabama operating under a council-manager or under a mayor-council-city manager form of government may, by a majority vote of the members of that governing body, adopt an ordinance establishing a council-manager form of government pursuant to the terms and conditions of this article. All provisions of this article set forth hereinbelow shall apply only to those Class 2, 3, 4, 5, 6, 7 or 8 municipalities electing to establish a council-manager form of government as set forth herein. This article shall be known as the “Council-Manager Act of 1991”.