I may be mistaken, but i'm pretty sure those Smitheys have tiny little cores that will choke a 383. Bad. If you want the glasspack sound, look into the "walker/dynomax/thrush" style. They have a straight through perforated core with no louvers and will give you that flappy raspy tone. Here are some, they come in alot of pipe sizes and lengths. Cheap too.
http://www.summitracing.com/search/S...rush+glasspack
They have stainless ones aswell on that link