This is a July 15th, 1988 case in the United States Court of Appeals, District of Columbia Circuit.
cite as 851 F2d 1439 (D.C. Cir. 1988)
Another lower court decision that discusses in depth the Oklahoma Indian Welfare Act (OIWA) - also discusses an interplay between the OIWA and the Curtis Act
Again the online opinions for the DC Appeals court only go back to about 1996 depending on which site you search.