In computing taxable income under section 63(a), the deductions provided by sections 212, 213, 214, 215, 216, and 217 shall be allowed subject to the exceptions provided in Part IX, Subchapter B, Chapter 1 of the Code (section 261 and following, relating to items not deductible). [T.D. 6796, 30 FR 1037, Feb. 2, 1965]