FWI Im using a ATR uppipe with Poston headers. Seals up fine with copper gasket at turbo (from ATR) and using a exhaust flange gasket that I picked up at Auto Zone at the header. I always thought the ATR pipe fitment was goofy and never could get it to seal until using the flange (donut) gasket.
If you go this route do a search in the Hotair section. Herb (TurboRegal84) was the one who told me about the flange gasket idea. I took it from there and may have posted a part# awhile ago, dont remember.