While Southern had quite a lot of older, wood cupola type cabooses in the 1940s and earlier, it appears as though when they bought newer, steel types they were all of the bay-window type. Hopefully an expert on Southern can give you a more definitive answer.
SOU cabooses with yellow bays were without larger radios and were normally found on locals and on branches such as we have here with the X205 at Union Springs, AL in 02/1984. That's a solar panel on the roof, used to charge walkie-talkies on longer runs. Another example, the X266 at Knoxville, TN on 02/10/1979: