FYI, I've had two different catbacks. I'm partial to the Dynomax catback kit for visual- and sound-related reasons, but mine rusted out after 5 years of mostly southern (GA and TN) driving. The Flowmaster kit I have on it now was free.
According to all the literature I've ever seen, in both parts catalogs and Flowmasters stuff, the resonator that was mentioned in an earlier post is for V-6's. It's not intended to replace the third cat or even the factory resonator that was used on the 5.0's and the 94-95 4.6. 2" inlets, and one 2.5" outlet. Has anyone tried to put it on a V-8 headpipe? It attaches to the catback, and I can't imagine why the headpipes wouldn't line up on either V-6 or V-8 cars.
The Flowmaster kit elimates the factory resonator on the 5.0's and the 94-95 4.6's. Dynomax's kit attaches at the back of the factory resonator or the pipe Ford installed on the 96-97's.
Anyway, the best thing you can do with a Flowmaster catback (once you are set on using it) is to paint it with some decent hi-temp paint. Black hides the system's visual issues pretty well. On my 97, I painted mine black when I installed it 4 years ago, and it still looks good (no visible external rust). The Flowmaster kit I put on my 92 Sport (back in 1993) looked terrible after about 6 months of use, with rust and dark spots all over it.
The goofy muffler outlet turndowns and the odd muffler angles aren't as noticeable with a SC rear bumper or a 96-97 rear bumper. "Straight", "plumb", and "level" just aren't in Flowmaster's vocabulary.
97 LX, 4.6, Dynomax catback, Mustang MAF/intake tube and Aviator throttle body, Xcalibrator2 by Lonnie at BOC, 180 t-stat, Super Coupe wheels with 235/60/16's, Kenny Brown strut tower brace, Tokico Blues, Eibach Pro-kit, some strategically placed MN12 Performance polyurethane pieces, '02 Grand Marquis transmission
Submariners do it deeper...