Beginning with the fiscal year next following May 24, 1939, not to exceed 75 per centum of the receipts derived in any one year from the Coos Bay Wagon Road grant lands in Oregon and deposited in the special fund in the Treasury created by the Act of February 26, 1919 (40 Stat. 1179), and designated "The Coos Bay Wagon Road grant fund" shall be paid annually, in lieu of taxes, by the Secretary of the Treasury, upon certification by the Secretary of the Interior, to the treasurers of Coos and Douglas Counties according to the ratio that the total assessed valuation of the reconveyed Coos Bay Wagon Road grant lands, belonging to the United States, in each of said counties bears to the total assessed valuation of all said lands in those counties, to be used for the purposes mentioned in said Act: Provided, That until such time as the general fund of the Treasury of the United States shall have been fully reimbursed by Douglas County for expenditures which were made charges against the Coos Bay Wagon Road grant fund by section 5 of the Act of February 26, 1919, said Douglas County shall be entitled to receive only 50 per centum of the amount to which it would otherwise be entitled under this subchapter: Provided further, That prior to making any payment under this authorization an appraisal of the land and timber thereon shall be made, within six months after May 24, 1939, by a committee to consist of a representative of the Secretary of the Interior, one representative for the two counties interested, and a third person satisfactory to the Secretary of the Interior and the county officials, but who shall not be an employee of the United States nor a resident of, nor a property owner in, either Coos or Douglas County. Upon appraisal thereof, the land and timber thereon shall be assessed as are other similar properties within the respective counties, and payments hereunder in lieu of taxes shall be computed by applying the same rates of taxation as are applied to privately owned property of similar character in such counties.