The only mod I know that actually does a Southern Victory right is Road to 56, and even then the South is still classified as Fascist. But I'm willing to overlook this because there's no political self-insert shit in Road to 56, so a Southern Victory is just as it would have been in real life, with the 11 secessionist states staying as the CSA, and the rest of the country still being part of the Union.
The only thing being Fascist does for the CSA is grant it earlier access to the Limited Trade economy law, make it easier/faster to declare war/send volunteers and lend-lease, and make it easier to get into the Reich's good graces. Again, it's not a political statement, it's just the modders giving the CSA a reason to exist as an "alternate start".
I'd shill for Road to 56 as a good "Vanilla+" mod, FYI.