Super Six HP gain?

Ok, so the exhaust, what will I need, and where do I find it?Transmission, should I be looking for a 904(there's one on craigslist that's sort of local it's a 904 Torqueflight from a 360), or 727?

TF 904 will be plenty...
either you have exhasut manifolds or headers and take it to an exhasut shop and have them make it...

or if you have the tools go by lengths of 2.5" .083 wall tubing and some u bends...