completed during any taxable year shall be made, under regulations prescribed by the Secretary, on the basis of engineering or architectural estimates or on the basis of cost accounting records. Unless the taxpayer establishes otherwise by clear and convincing evidence, the conversion shall be deemed to be completed not more rapidly than ratably over the normal conversion period. (E) No progress expenditures for certain prior periods No qualified conversion expenditures shall be taken into account under this subsection for any period before the first day of the first taxable year to which an election under this subsection applies. (F) No progress expenditures for property for year it is placed in service, etc In the case of any building, no qualified conversion expenditures shall be taken into account under this subsection for the earlier of— (i) the taxable year in which the building is placed in service, or (ii) the first taxable year for which recapture is required under section 50(a)(2) with respect to such property, or for any taxable year thereafter. (4) Self-converted building For purposes of this subsection, the term self-converted building means any building if it is reasonable to believe that more than half of the qualified conversion expenditures for such building will be made directly by the taxpayer. (5) Election This subsection shall apply to any taxpayer only if such taxpayer has made an election under this paragraph. Such an election shall apply to the taxable year for which made and all subsequent taxable years. Such an election, once made, may be revoked only with the consent of the Secretary. (e) Denial of double benefit A credit shall not be allowed under this section for any qualified conversion expenditure for which a credit is allowed under section 42 or 47. . (c) Conforming amendments (1) Section 49(a)(1)(C) of the Internal Revenue Code of 1986 is amended by striking and at the end of clause (vii), by striking the period at the end of clause (viii) and inserting , and , and by adding