85firebird

i have tried posting this on thirdgen.org but no one knows about this i gess. maby over hear you guys could help me, i have a 1985 firebird and i am putting a new 350 in it and going to put a whole new exhast in it. since i live in CA and have there stupid emissions the exhaust has to exit the back of the car. what i was looking at is doing true duals from the headers back 2 1/2 piping all the way back of the car thew chambered mufflers at stainless steel works(same ones GMMG uses for theres,im pretty sure.)There will be 2 cats used for that.Or 3' ORY into GMMG exhaust. My question is what will sound better,what would be cheaper, which would get better power gains. the shop that i am going to get it done at will be providing all the piping so i don't have any of it. i was also thinking of just using a bullet muffler also i don't know though what do you guys think.