26 C.F.R. § 1.9004-3
The period within which the assessment of any deficiency or the credit or refund of any overpayment attributable to the election may be made shall not expire sooner than one year after December 11, 1961. Thus, if assessment of a deficiency or credit or refund of an overpayment, whichever is applicable, is not prevented on September 26, 1961, the time for making assessment or credit or refund shall not expire for at least one year after December 11, 1961, notwithstanding any other provision of law to the contrary. Even though assessment of a deficiency is prevented on September 26, 1961, if commencement of a suit for recovery of a refund under section 7405 of the Internal Revenue Code of 1954 may be made on such date, then any deficiency resulting from the election may be assessed at any time within 1 year after December 11, 1961. If a taxpayer makes the election, he shall be deemed to have consented to the application of the provisions of the Act extending the time for assessing a deficiency attributable to the election. The Act does not shorten the periods of limitation otherwise applicable. An agreement may be entered into under section 6501(c)(4) of the Internal Revenue Code of 1954 and corresponding provisions of prior law to extend the period for assessment.
26 C.F.R. §1.9004-3
75 Stat. 674; 26 U.S.C. 613 note