Stand Watie commanded the 1st Cherokee Mounted Volunteers and had nothing to do with the 1st Choctaw & Chickasaw Mounted Rifles - not even after he was made Brigadier General (his brigade consisting of Cherokee, Creek, and Seminole troops). The 1st Choctaw and Chickasaw Mounted Rifels was commanded by Colonel Douglas H. Cooper and afterwards Tandy Walker.
Jonathan Nail was Major of the Chickasaw Battalion from October 1864. Captain Adam Nail commanded Company A of the 1st Choctaw & Chickasaw Mounted Rifles.
I am not aware that Stand Watie at any time maintained his headquarters at Fort McCulloch. What do you base that on?