As I recall, the Leach and Avery plant was very near the Tuscaloosa-to-Northport covered bridge, on the banks of the river. There is a local history book that gives a description of its location (again, as I recall off the top of my head). I may have a copy of that page in my file. If I find it, I'll post a more complete description of the location.
I don't know where the others were located.