I have a '96 4.0 and I changed mine to duals about 3 months ago. Not true duals though.
the Y pipe comes down and goes into a single magnaflow high-flow cat (there were two when I started), the pipe from there on back is 2 1/2 inch, which goes into a Magnaflow single-inlet dual outlet muffler, the pipes off the back of the muffler are 3 inch I think and it ends in dual 3 1/2 inch tips. The tips dump a few inches in front of the right rear tire, which makes the pipes from the muffler to the tips very short.
Overall it sounds alright, gives off a V8-ish sound at idle and it sounds quite growly under 2,500RPM... anything over that and it starts to sound a little rice-ish. The only annoying part is when I change gears fron first to second, sometimes from second the third, it has a tendency to generate a "fairy poof". Thats my only complaint really, can't ask for much better from a smaller motor.