LSG

390,  our friend Mr Barnett is only right on two things. 1, 'sounds good' is very subjective. I might not like what you like, and you might not like what I do. and 2, its complicated. Thats as far as it goes. Unfortunately, there are a great many people like our friend  who don't understand the difference between primary and secondary exhaust tubing.  Primary exhaust pipes are very much size critical, diameter and length both matter. Once you get past the collectors, however, open atmosphere is best. Most of us don't want to listen to open headers all day everyday, so we install a system.  In that system, the SECONDARY pipes can't be too big. There just isn't any such thing. However, if you search the 'net, you can find lots of stories and opinions about people going faster after switching from 2 &1/2 or 3 down to 2 &1/4th or 2. What these folks fail to realize is that if their car was jetted and timed properly, they would be faster and make more power with the larger secondaries. Maybe they don't know how to read plugs or change jets. So, why do some folks, even exhaust manufacturers, recommend the smaller stuff ? That part is simple, it is easier and cheaper to make. When an exhaust shop tells you that a smaller secondary makes more power 'down low', what he is really saying is that does not  have a 3 inch mandrel to bend the larger pipes with, and doesn't have the needed skill to hang a 3 inch system.  And our friend is wrong about it being tough to fit. It fits fine, it is tight,but you CAN do it, Just get the Magnaflow stuff and put it on. I would recommend reversing the bolts on you rear spring shackles, it give you more room for the 3 inch pipe, AND for your fingers as you are working. If you look around this site, you should find a thread from one of our men who made his own twin outlet tips to fit his 3 inch exhaust. Looked just like stock, only bigger. You might also check Buckeye Demon's build thread. He has a 351W based engine with a custom 3 inch system. Looks nice. And I haven't heard him complain that it was 'too big'. Also keep in mind that the secondary pipe diameter affects tone. A bigger pipe is not 'louder' as some folks presume, but DOES  have a lower tone, which many folks find easier and more tolerable on the ears.    LSG

390, look at the MagnaFlow 3 inch kit. The only thing you'll have to do is make your own tips, if you want to replicate the M1 original outlets. There is no reason to choke it down to 2 & 1/2 after the mufflers. Stay at three. Don't listen to anyone who tells you that 3 inch is 'too big' , it isn't. After the header collector, there is  no such thing as too big. The only reason I didn't buy from them is MF will only sell the full kit, even though I only need the tailpipes.  If they were willing to sell me 3 inch tailpipes alone, I'd buy them in a hot second.   LSG