Civil War US Colored Troop Pension Records

Hello! I am trying to find the actual file for Frank Wallace who enlisted in 1864 in Natchez, Mississippi, and served in Co. M, 6th US Colored Heavy Artillery.  According to the Civil War Pension Index reference card, there was an application #707301; certificate # 584958, as well as a widow's application #960716; certificate #751734.  There is also a number: XC 980142 appears in the remarks section.  

Any assistance would be appreciated.  Thank you!