I have the Langdon cast headers into two 2" duals with 20" steel pacs with the louvres facing exhaust flow. As far as loud goes I'd give them a 7 on a 10 scale. Here are two videos of my car that may help you.
http://www.youtube.com/watch?v=4FchcwJXU-o&feature=related
http://www.youtube.com/watch?v=kvP5FyVnVg4&feature=channel


Martin
'64 Nova wagon
'69 C10