Some years ago, I did research on some 56th USCI troops from Southeast Missouri,formerly known as the 3rd Arkansas Inf, African Descent. Dyer's "Compendium of the War of the Rebellion" pg. 1732 incorrectly lists this as an Alabama unit. Research for these troops is daunting as some did not use the surname of their masters when enlisting.
I can point you to a couple of sources you may find interesting on the 56th at the WHMC-Columbia, Collection #'s C995-215 and C#995-516 both on film and available thru inter-library loan. I thoroughly enjoyed reading "Freedom-A Documentary History of Emancipation 1861-1867" Series II The Black Military Experience and you may find this in a larger library. Series II pg. 227-28 contains an interesting account of a Southeast Mo. farmer's complaints that soldiers of the 3rd Mo. Cav. were recruiting negroes, literally from the fields. This in June 1863.
My research is 10 years old, probably many other sources available now. Let me know if I can help you.