OK, here l go again with a list of questions.
1) Do l need to take off the cats when getting a y-pipe? Or can it work with cats, if so how much hp will it increase?
2) Do 350Zs come with resonators? lf l take them off, will it give me power?
3) Where is the best place to get aftermarket parts?
4) l live in Duluth, GA (near Atlanta) and does anyone know a trusty mechanic that can install aftermarket parts?

 

1) No you don't take off the cats, and it depends on the exhaust as to the HP increase. Maybe 10(?)
2) Yes, do a search for "pre-silencer", and as far as gains probably not. It may sound "better" though.
3) Depends on the part. Search the forum for the part you are looking for.
4) Do a search.

 

So it boils to three options : 1.) Do a search.
2.) Do some more searching.
3.) Still do some more searching.