In construing this act, port districts coterminous with a city or township shall follow the same procedure as is prescribed for counties, substituting the local governing body and officers where applicable for the board of supervisors and county officials. Whenever in this act any power is granted to a port district, it shall be exercised by the port commission unless otherwise provided herein. Whenever in this act any power is granted to a port commission it shall be deemed to be granted to the port district but to be exercised by such port commission.