Have you tried looking at denominational newspapers? I did a project on Presbyterian schism in the Southern United States around that period some years ago and found a number of Presbyterian magazines and newsletters to be helpful. I imagine other denominations were publishing similar material. Since so many churches had Civil War related splits that weren't resolved by the interwar period (Presbyterians, Baptists, Methodists, and so on) those denominational publications might useful -- though of course they wouldn't necessarily be representative of a wide spectrum of religious practice in the region.

You may find the Encyclopedia of Alabama to be a helpful starting point. It is published online here.

Also, have a look at Wayne Flint's Alabama in the Twentieth Century. He has a chapter on religion late in the book, though he focuses on the state constitution as the source of the problems he discusses. In addition, his book on Alabama Baptists focuses only on that one denominational family, but could be quite helpful anyway. (I have a personal connection to Dr. Flint as well; if you think reaching out to him would help send me a private message, though really you could just do it.)

FWIW, the religious landscape of Alabama has always been more diverse than many people would expect, and the time and page count it takes to get a handle on the whole thing even within a brief period such as you describe could be large.