go with the SS headers and the random SHF (super high flow) metal matrix 3" cats. they can slip right on the collectors and make for a very neat install and don't cost much hp (3-5) if you need cats.
look for deals if you want stock manifolds, so many folks have upgraded you can get them at a decent price, 4-800 is common. new from GM they were stupid expensive.
the factory 90 manifolds are terrible. they pinch at the pipes going into one big tube before the cats and yes, they are one big welded part.
callaway did the "chief" manifolds which eliminated the pinch and worked better with a factory looking design. hard to find.
do the SS headers from stainless work (brian a. carries them too) and be done with it. you will love the way the car picks up.
