The articles of a limited dividend housing corporation may authorize the issuance of income debenture certificates bearing no greater interest than six percent per annum. After the incorporation of a limited dividend housing corporation, the directors thereof may, with the consent of two thirds of the holders of any preferred stock that may be issued and outstanding, offer to the stockholders of the company the privilege of exchanging their preferred and common stock in such quantities and at such times as may be approved by the director for such income debenture certificates, whose value shall not exceed the par value of the stock exchanged therefor.