Actually not a kool sounding muffler but wait till you hear the gas mileage increase! I measured the diameter of the pipe from the back of the CAT converter and end of the muffler for my I6 engine. It's 2 1/4" out the CAT and 2" out the muffler. It also has the center input and offset output. I ordered the 2 1/4" at both ends Dynomax Stainless Steel Super Turbo
muffler from JC Whitney.
It's a super deal at $99. and if you get their magazine you should be able
to get 10% off with a coupon. Remember you'll pay shipping
so if you want to check around other stores. When it arrived I checked
it out. The advertisement on the box said "straight through design".
They weren't kidding as the front tube is attached to the back tube with
a S/S slightly curved tube. I looked a the loudness advertisement
on the box and it was much quieter then others listed. I figured
this was going to be real noisy and would have to add a tail pipe glass
pack addition . I purchased this muffler against another as it was
almost as big as the giant muffler on the ZJ.
I figured taking off a S/S muffler can't be that hard, no rust. I did need to heat, with a torch, the front muffler clamp to get it off. That was saved as it was a Sunday afternoon I didn't have spare clamps and stores were closed. I cut the pipe behind the muffler off with my Sears reciprocating saw & metal cutting blade. I cut about 2" from the back of the muffler leaving some 3" remaining on the tailpipe. The rear 2"OD pipe behind the muffler was straight so I figured I should be able to get an adapter on there. I did not use the large pipe that fit both ends. The inside of the 2"ID would not fit over the S/S tail pipe, it was getting dark, tried the following. Taking off the muffler, as you saw from the picture, was not easy. I could wiggle the muffler but it wouldn't slide back. I resorted to a 5 lb. sledge hammer. Even with that I still had to cut the front part of the muffler away from the CAT with my air gun.
Finally it came sliding off, there is about 4" of pipe at the end of the
CAT. When you place the center part of the
muffler on the CAT it will not slide in all the way as the inside parts
of the muffler prevents it. You could cut off some of the end of
the CAT but I didn't.
I also added a S/S muffler strap from JC Whitney ($7)
to connect 2 - 2" OD (0utside diameter) pipes together. I just in
case I sell the car, I'll put back the old muffler. This muffler
strap would allow that. I found a 2 1/4 muffler adapter with the
other end a 2" OD. I happen to have a 2 1/4 OD pipe so I cut this
pipe to fit inside the muffler and the adapter pipe. Two spare muffler
clamps held them in place. I used this S/S
strap 
to
reattach the tail pipe and adapter. These adapters are steel parts,
not S/S, so some 4 years from now they may rust out. The S/S strap worked
fine (no leaks) but they would not support the weight of this large muffler.
The strap flexed a bit as the welded S/S tail assembly only has one hanger
at the rear. No other support for the muffler/CAT existed.
I added a $1 muffler hanger from PEP BOYS,
an exposed bolt right under the muffler would support the strap.
I bent the hanger strap, below the second hole, at the top. I
fit the hanger clamp between the two muffler clamps.
Now the muffler was not flexing the S/S strap. The tailpipe is up
a bit in the rear but I haven't heard it hitting.
I started the car expecting a loud rumble, worse than my '86 Fiero, but that car sounded pretty cool. Nothing.... nope... the I6 engine sounded as it has the standard muffler on it. My van sounded louder that this straight through muffler.