Here's a more recent thread where I posted a few locations where you can hear Sacred Harp on the web.

I think guest's African American tradition is referring to 7 shape gospel. If not & it's the 4 shape, I'd like more information. In the past the 4 shape tradition was strong in the rural south among both Anglo & African Americans. A few small African American groups are active in Alabama and Mississippi, but they seem to be aging very rapidly with not many young people still participating.