Sorry, I didn't read through the whole thread, but here's my opinion....

The R/T downpipe uses a donut gasket and springs on the manifold bolts to allow the downpipe to flex as the engine moves around.
This has caused problems for a lot of people (they leak), and I would recommend checking out one of the downpipes that use a flex section near the top of the downpipe to allow for engine movement.
The Hogan downpipes, the W-body store downpipes, and the ZZP downpipes all have the flex section and are much less likely to leak.

-Riggs.

Here are a couple of pictures of a 2.5" 304 stainless steel bolt in with cat from ZZP

http://i33.photobucket.com/albums/d5...pipe_front.jpg
http://i33.photobucket.com/albums/d5...npipe_rear.jpg
http://i33.photobucket.com/albums/d5...p_exithole.jpg
http://i33.photobucket.com/albums/d5..._fronthole.jpg