are yo ugoing single or dual out? are you putting all new pipe from the cat to the tailpipe?? I'd suggest 2.25" or even 2" all the way back for your 3.0L....if your doing single. You need a side/center muffler......so Offset inlet/center outlet. If dual, i'd do 2.25 in, dual 1.75 or 2" out. I suggest the super 44, it's a super40 but in a smaller case. I got better mileage out of my Super 40 than my current Original 40. But then again, my Super 40 had a tailpipe, and my current Original 40 is dumped w/o a tailpipe.
'01 XLT disguised as a '03 Fx4 Level II
Big. Loud. Slow. Bright.