882's flow fairly decent for a factory smog head, and many people have used them in similar buildups. Just be aware that they are thin castings and will easily crack if overheated.
As for the gaskets, Ive never used them so Im not sure. But ive never had a problem with the regular header gaskets on any set of headers Ive run. I think people dont keep the header bolts snugged down and this is the problem. They have to be checked often.