(a) Upon the taking effect of this subchapter, pursuant to section 618i of this title, the charges, or the basis of computation thereof, promulgated under this subchapter, shall be applicable as from June 1, 1937, and adjustments of accounts by reason thereof, including charges by and against the United States, shall be made so that the United States and all parties that have contracted for energy, or for the privilege of generating energy, at the project, shall be placed in the same position, as nearly as may be, as determined by the Secretary, that they would have occupied had such charges, or the basis of computation thereof, and the method of operation which may be provided for under section 618h of this title, been effective on June 1, 1937: Provided, That such adjustments with contractors shall not be made in cash, but shall be made by means of credits extended over such period as the Secretary may determine.

(b) In the event payments to the States of Arizona and Nevada, or either of them, under section 618a(c) of this title, shall be reduced by reason of the collection of taxes mentioned in said section, adjustments shall be made, from time to time, with each allottee which shall have paid any such taxes, by credits or otherwise, for that proportion of the amount of such reductions which the amount of the payments of such taxes by such allottee bears to the total amount of such taxes collected.