John,
Before you get too excited about the GN1 dump pipe or test pipe, I thought I'd let you know I really don't think it's constructed of T304 stainless as advertised. I just checked mine and a magnet sticks to it like crazy. The exhaust system he sells is T304 and the downpipe is T304 for the most part (magnet sticks a bit harder on the bends and especially at the turbo flange and wastegate flanges). The dump pipe might not even be low grade stainless though. I would really have taken issue with Archie at GN1 about that had he not given me the dump pipe for free for buying the whole system at once. Maybe Eticket's ATR dump pipe/test pipe isn't such a bad deal after all...