26 C.F.R. § 1.875-2

(a) [Reserved]

(b) Exception for certain taxable years. Notwithstanding paragraph (a) of this section, for any taxable year beginning before January 1, 1975, the grantor of a trust, whether revocable or irrevocable, is not deemed to be engaged in trade or business within the United States merely because the trustee is engaged in trade or business within the United States.

(c) [Reserved]