; (ii) section 215(b) as in effect in December 1978 shall apply, except that section 215(b)(2)(C) (as then in effect) shall be deemed to provide that an individual’s computation base years may include only calendar years in the period after 1950 (or 1936 if applicable) and ending with the calendar year in which such individual attains age 61, plus the 3 calendar years after such period for which the total of such individual’s wages and self-employment income is the largest