Upon the organization, reorganization or reconstitution of any special municipal separate school district, the board of supervisors of the county wherein such special municipal separate school district is located and the governing authorities of the municipality may, by an order spread upon their minutes within sixty days after such organization, reorganization or reconstitution shall have become final, expressing an agreement between both such governing authorities, choose to constitute the board of such special municipal separate school district under one of the optional methods of organization set out in Section 37-7-717. In the event that both the governing authorities hereinabove referred to shall enter such an order within said period, then the said board of trustees shall be thereafter constituted and selected according to the terms of such agreement, provided such agreement is in conformity with the terms of Section 37-7-717. It is further expressly provided that irregularities of a procedural nature in the adoption of such orders shall not affect the validity of the same or the validity of any acts of the board of trustees which may be constituted by virtue thereof.