Little tidbit, if we are talking about Southern Democrats who voted for Reagan (and possibly Republican after that), they absolutely did not defect until 1984. Jimmy Carter dominated the rural South in 1980 and only (barely) lost the Southern states that he did because Reagan won the more populated counties...
The only Southern States Jimmy Carter won in 1980 were his home state of Georgia and West Virginia. It is true that he lost many of them by around 1-2%.
I'm aware, but 1) the South was still Carter's best region and 2) if you look at the county results, Carter dominated the rural South while losing the suburban vote (which was already trending Republican in the 1950s and especially since the late '60s) ... I think it's pretty obvious that most "Yellow Dog Democrats" that we tend to picture when we talk about old Southern Democrats stuck with Carter in 1980 and didn't defect until 1984.
