Z Code, I haven't tested it myself. I do recall that when Jim Hand tested mufflers years ago, he tested them as single exhaust on his 455. He did this to make the difference more noticeable. This always gave me the impression that most good dual systems would flow plenty for a smaller street engine. I know it's not a very helpful post but it's something that suprised me, the single exhaust thing.
That info used to be somewhere on the net. Maybe someone can post a link. It was in HPP yrs. ago.
Later, Murf
Here it is,
http://www.pontiacstreetperformance....p/exhaust.html