Any elective official of the state of Iowa, or any of its political subdivisions, who becomes subject to federal social security coverage under the provisions of the agreement referred to in section 97C.3 shall, not later than October 1, 1953, pay into the contribution fund established by section 97C.12 a tax sufficient to pay in the elected official’s behalf an amount equal to three percent of the official’s compensation received as a public official for each year or portion thereof that the public elected official has served as a public elective official since January 1, 1951, not to exceed thirty-six hundred dollars for any year of service. The state agency shall collect the tax hereby imposed and the proceeds from such tax shall be used for the purpose of obtaining retroactive federal social security coverage for elective officials, for the period beginning January 1, 1951, in the same manner as is provided in the case of other public employees by the provisions in section 97.51, subsection 2, in order to obtain retroactive federal social security coverage during this period of time, such contribution to be collected and guaranteed by the employer. The state agency will pay any such amount contributed to provide for retroactive federal social security coverage for the individual in question in the same manner as other payments are made for retroactive coverage of public employees. Provided that no member of a county board of supervisors shall be deemed to be an elective official in a part-time position, but every member of a county board of supervisors shall be deemed to be an employee within the purview of this chapter and shall be eligible to receive all of the benefits provided by this chapter to which the member may be entitled as an employee.