In the case of a specific rate (or of a combination of rates which includes a specific rate), the one-half of 1 per centum specified in clause (ii) of the preceding sentence shall be determined in the same manner as the ad valorem equivalent of rates not stated wholly in ad valorem terms is determined for the purposes of paragraph (2)(D)(ii) of this subsection.
The provisions of clauses (ii) and (iii) of this subparagraph and of subparagraph (B)(ii) of this paragraph shall, in the case of any article, subject to a combination of ad valorem rates of duty, apply to the aggregate of such rates; and, in the case of any article, subject to a specific rate of duty or to a combination of rates including a specific rate, such provisions shall apply on the basis of the ad valorem equivalent of such rate or rates, during a representative period (whether or not such period includes July 1, 1958), determined in the same manner as the ad valorem equivalent of rates not stated wholly in ad valorem terms is determined for the purpose of paragraph (2)(D)(ii) of this subsection.