IF it were "I" doing this project, then a look around the net for comparisons is the first step.
Being in this exact position, only with a 360/5.9 Magnum engine in my car, I have looked around and searched for a quiter system myself. I have used the Jegs turbo mufflers (in there exhaust kit for my 318 Duster) and found them to be pretty good. There a chambered turbo muffler. Who makes the system for Jegs I do not know. I still want better. And bieleve me it was pretty good. The endeavor has lead me to try and think before I leap.
For your set up, headers off the /6 into a "X" pipe is what I would do. But do you want two mufflers? Dyno Max has a single muffler that has an internal "X" built in. This would save some good coin in fabrication and a little bit of a headache in trying to do one yourself. The muffler is good for 400HP according to them. They are available in 3 - 2-1/2 & a 2-1/4 which would be good for you.
If you wanted two mufflers, and quite ones, after the "X" pipe, I'm going to try the Dyno Max VT's. Should the sound levels not be met inside the cabin, adding there round straight through glass pack muffler is something I have looked into. What is nice about there glass pack muffler is the inside of the tube does not neck down.
There sound absorbtion (sp?) muffler takes on the high notes very well and places a damper on the low. Doing these before the main muffler reduces interior sound as well as the exterior sound. Placing them after the mufflers reduces exterior sound only. Dyno Max says 4db worth. And no flow reduction.
Just how my engine exhaust note sounds in my car will determin there placement If needed.
Adding a sound deadening mat under the carpet will help a good bit. More the merry. If only a little bit is desired, then just so the rear half of the cars cabin. Start about where the rear seat bolts to the floor and go back as far as possible. This will help a lot.
The comment of lighter weight equals going fast should be know As true but ignored at this point due to the low power output of the car. Getting rid of 100lbs. On your car would be a bonus but extremely hard pressed to see, feel and note any differences in performance.
You'll only (possibly) note it at a drag track if your consistent enough to to measure it due to your extremely excellent light cutting ability and stupidly insanely consistant running car.
