26 U.S.C. § 7807: Rules in effect upon enactment of this title

Until regulations are promulgated under any provision of this title which depends for its application upon the promulgation of regulations (or which is to be applied in such manner as may be prescribed by regulations) all instructions, rules or regulations which are in effect immediately prior to the enactment of this title shall, to the extent such instructions, rules, or regulations could be prescribed as regulations under authority of such provision, be applied as if promulgated as regulations under such provision. Any provision of this title which refers to the application of any portion of this title to a prior period (or which depends upon the application to a prior period of any portion of this title) shall, when appropriate and consistent with the purpose of such provision, be deemed to refer to (or depend upon the application of) the corresponding provision of the Internal Revenue Code of 1939 or of such other internal revenue laws as were applicable to the prior period. If an election or other act under the provisions of the Internal Revenue Code of 1939 would, if this title had not been enacted, be given effect for a period subsequent to the date of enactment of this title, and if corresponding provisions are contained in this title, such election or other act shall be given effect under the corresponding provisions of this title.