+1 on the header-back 2.5" system. i did this and am very, very pleased. sound is amazing and will make you feel like speed racer every time you pull past 4K rpm
here's my thread on this - there are many others as well:
http://www.classiczcars.com/topic/49967-2-12-shop-built-exhaust-sounds-great/?hl=2.5
bolt-up systems are available, but for the price you can get a custom setup fabbed and have it exactly like you want.
find a good mom-&-pop muffler shop and you can do the whole thing for $200-$400 including the resonator in the tunnel, muffler and tip. alumanized steel is fine for the pipes, as they don't hold water much and will last plenty long - mandrel bent is best for free-flow, go with stainless resonator and muffler, as they are the first to rot out, then get a polished stainless tip which will look beautiful forever. much has been written about using a tip that turns down and sticks out a bit farther than the rear bumper to help get exhaust out of the airstream so it doesn't pull back into the cabin.
lots of threads on this - of course a simple muffler swap will change the sound, but it's a pretty small step up to do the whole thing and be very, very happy.