Thunder has a new version out, and there is a group buy going on right now so if you PM Protephile he may have an extra spot. MAM is by far the best for our car according to dyno sheets, but they are hard to find. Also, 505 did not make a turbo manifold, only an intake manifold. Though if you get one of those you would be a happy camper.
The easiest way to install a new downpipe is to remove the manifold, turbo and s-pipe all at once. That way you can bolt them together out of the car, then just mount it to the block, hook up the turbo lines and bolt the exhaust together and BAM instant sexiness.