340 Dart GTS Headers

Hi Guys
I have been reading all the posts about Headers...Heaven forbid I use Hookers!!! Not interested in having to attend anger management courses relating to 50 cal. machine gun usage!
Anyway my questions are:
1. Which brand would be best fit on my 69 Dart GTS with a stock340, power steering!
2. What are the best sources for these products
3. What are the preferred mufflers for your preferred headers
I have something LOUD on there now (came with the car) and I have not been able to determine what brand they are, no easily viewable embossment on the mufflers themselves.

A related question, what is the round valve like apparatus on the right stock manifold that lets the exhaust "blow by"? It never closes and it creates extra noise not to mention exhaust fumes in the engine compartment and front of the car???? It is located just forward of where the manifold connects to the exhaust pipe.
Thanks for the help
Darius
69 Dart GTS