You misread. Check out the various specifications on Chevy's website or any other thread, or re-read that same thread again. No V8 will have an open diff. It's in the PDF in this thread:
http://www.camaro5.com/forums/showthread.php?t=7790
Search the PDF for "limited". The first hit will be the V6 equipment page, where it says MT only. The second hit will be the V8 page.