In the case of any plan maintained on January 1, 1974, if not later than 2 years after September 2, 1974, the administrator petitions the Secretary, the Secretary may prescribe an alternate method which shall be treated as satisfying the requirements of section
1053
(a)(2) or
1054
(b)(1) (other than subparagraph (D) thereof) of this title or both for a period of not more than 4 years. The Secretary may prescribe such alternate method only when he finds that—
In the case of any plan with respect to which an alternate method has been prescribed under the preceding provisions of this subsection for a period of not more than 4 years, if, not later than 1 year before the expiration of such period, the administrator petitions the Secretary for an extension of such alternate method, and the Secretary makes the findings required by the preceding sentence, such alternate method may be extended for not more than 3 years.