The mountainous regions of the Confederacy were pro-union in the main. A county in north Georgia is called Union County. Most of the residents there hid out to avoid the war, including most of my kin apparently. Eastern Tennessee was very pro-Union, so perhaps Tennessee should go to the B1G.
I would disagree that Virginia was largely occupied during the Civil War. Parts of it were for sure, near Norfolk and near DC in the main.
The ACC obviously spans any Mason-Dixon demarkation, which of course just defines the MD-PA border, it doesn't not extend west at all.