Hey i have a 1991 z28 5.7. I would like to keep the dual cat idea going in my car, but i want to upgrade the entire thing to a 3'' system because ill be building up my engine after i figure this out. I cant seem to find any specific threads addressing what headers go where or how to do this. so what parts are good for this? what will i need to look into?

What are you overall engine plans for car? 3" should be good to 350hp. If you want to keep dual cats, best option may be to buy good performance headers (short or long style) and muffler. Then have local shop connect header to cats and to muffler with mandrel bent tubing. You can also buy sections of exhaust pipe to fab it up yourself.
Check out this thread.
http://www.thirdgen.org/techboard/ex...ion-chart.html (Thirdgen Header option chart - explained)

Hedman makes headers with dial "y-pipe". Jegs has it for $380.
http://www.jegs.com/i/Hedman/500/68491/10002/-1#
http://www.hedman.com/products/?id=3538&rsku=5216

Edlebrock has TES headers for dual cat cars.
http://www.edelbrock.com/automotive_..._tes_app.shtml