Dynomax super turbo muffler size

I can swing by and you can hear my exhaust on the Duster.
remember it is a stock '79 318 with bolt on's and a small Crane cam.
Or, this could be good enuff for you;

http://www.youtube.com/watch?v=pOYMlTTecTU

The cars engine was a little cold as you can tell be it loading up a bit.