Section, added Pub. L. 85–866, title II, § 206(a), Sept. 2, 1958, 72 Stat. 1681, § 6166; amended Pub. L. 93–625, § 7(d)(2), (3), Jan. 3, 1975, 88 Stat. 2115; renumbered § 6166A and amended Pub. L. 94–455, title XIX, § 1906(b)(13)(A), title XX, § 2004(a), Oct. 4, 1976, 90 Stat. 1834, 1862, provided for an extension of time for payment of estate tax where estate consists largely of interest in closely held business.