(a)Taxable years beginning before September 13, 1966, and ending after September 12, 1966—(1) General rule. An election made under section 615(e) or section 617(a) applies only to expenditures paid or incurred after September 12, 1966. The income tax treatment of exploration expenditures paid or incurred before September 13, 1966, will be determined in accordance with the provisions of section 615 prior to its amendment by the Act of September 12, 1966 (Pub. L. 89-570, 80 Stat. 759). If a taxpayer makes an election under section 615(e) in his income tax return for a taxable year beginning before September 13, 1966, and ending after September 12, 1966, amounts deducted under section 615 with respect to expenditures paid or incurred during such taxable year but before September 13, 1966, will be taken into account in determining whether the $100,000 limitation set forth in section 615(a) is reached during 1966. Similarly, a taxpayer making an election under section 615(e) shall take into account expenditures deducted under section 615 for periods prior to September 13, 1966, in determining when the $400,000 overall limitation set forth in section 615(c) is reached. The fact that a taxpayer deducts under section 615 expenditures paid or incurred prior to September 13, 1966, shall not affect his right to make an election under section 617(a) to deduct under section 617 expenditures paid or incurred after September 12, 1966.