(a) In general. Section 206(f) of the Small Business Tax Revision Act of 1958 (72 Stat. 1685) provides that section 6166(i) of the Code shall apply in cases where the decedent died after August 16, 1954, but only if the date for filing the estate tax return (including extensions thereof) expired before September 3, 1958. Therefore, the privilege of paying the estate tax in installments as described in §§ 20.6166-1 through 20.6166-3 is available also in cases where the due date of the return is before September 3, 1958, but under somewhat different circumstances. These differences are explained in paragraphs (b) through (e) of this section. Therefore except as otherwise provided in paragraphs (b) through (e) of this section, the regulations contained in §§ 20.6166-1 through 20.6166-3 apply also in cases where the due date of the return is before September 3, 1958. See § 20-6075-1 for the due date of the return. The value of the gross estate as determined for purposes of a deficiency in tax assessed after September 2, 1958, and the value at which the interest in the closely held business, to which the election applies, is included in such value of the gross estate are used in ascertaining whether an estate coming within the purview of section 6166(i) and this section satisfies the percentage requirements as to qualification set forth in section 6166(a).

(b) Tax to which election applies. In a case where the due date of the return was before September 3, 1958, an election to pay estate tax in installments does not apply to the tax shown on the return nor to a deficiency in tax assessed before that date. It does apply to a deficiency in tax assessed after September 2, 1958, unless the deficiency is due to negligence, to intentional disregard of rules and regulations, or to fraud with intent to evade tax. The amount of the deficiency which may be paid in installments shall not exceed that proportion of the total tax (including the deficiency) which is determined by applying thereto the ratio set forth in paragraph (b) of § 20.6166-1. See paragraph (c) of this section for the method of prorating the deficiency to the installments.

(c) Proration of deficiency to installments. The deficiency in tax which may be paid in installments is prorated to the installments which would have been due if the provisions of section 6166(a) had applied to the tax shown on the return and if an election had been timely made at the time the estate tax return was filed. The part of the deficiency so prorated to any installment the date for payment of which would have arrived before the election is made shall be paid at the time the election is made. The portion of the deficiency so prorated to installments the date for payment of which would not have arrived before the election is made shall be paid at the time such installments would have been due if such an election had been made.

(d) Notice of election. The notice of election to pay the deficiency in installments shall be filed with the district director not later than 60 days after issuance of notice and demand by the district director for payment of the deficiency. The number of installments in which the executor elects to pay the deficiency includes those installments the dates for payment of which would have arrived within the meaning of paragraph (c) of this section. See paragraph (e)(2) of § 20.6166-1 for further information relative to the notice of election.

(e) Undistributed income of estate. In any case where the due date of the estate tax return was before September 3, 1958, the provisions of paragraph (b) of § 20.6166-3 (providing for acceleration of payment of estate tax by amount of estate's undistributed net income for any taxable year after its fourth taxable year) shall not apply with respect to the estate's undistributed net income for any taxable year ending before January 1, 1960.