I went with a 20" case, Offset Inlet, and a Center Outlet. That was recommended to me by another member who used the Super turbo. It fits just fine where the old muffler was.
I also went with a 2.50 inch pipe which is slightly larger than stock. For the record I am not sure what diameter the stock exhaust pipe is, but I am sure someone here knows. (I THINK it is 2.25")