Seeking records of Inspector General, XX Corps, in RG 338.9.3

I am researching my uncle Cyril B. Spicer, Sr. (1891-1971) whose headstone reads HQ XX Corps. He was an Inspector General per his retirement records in the Army Registers. XX Corps was one of Patton’s Third Army corps and I have other references (newspaper and family memories) to him working for General Patton. It would seem that any additional research would be in RG 338.9.3 but I’m wondering if there would be any other records for Inspector Generals in the WW2 era. And if there are any Finding Aids to 338.9.3 or any other records that might apply.