The form of government provided in this subchapter shall be known as the "Small Municipality Plan." It may be adopted by any municipality having a population of less than 7,500 inhabitants by the last Federal census. The plan, together with Subchapter F of Chapter 29 (relating to general provisions and limitations for optional plan municipalities) and Subchapter A of Chapter 31 (relating to officers and employees), shall govern any municipality the voters of which have adopted it pursuant to this subpart.