[DGFourSixLX]

Ok...
To begin, you will likely have an advantage either way if you cut off that useless 3rd converter. I know of people who run these cars with hollowed out converters and pass emissions (in MA anyway). If you like the way a Mustang sounds with Flowmasters, here is one solution. Cut off the 3rd cat. Run it dual back to a Flowmaster 40 series dual 2.25" in/out where the stock resonator is now. From that, bend the new 2.25 pipes to follow the route of the original system, and do any type of exit you wish. An upside to this is that you won't have to weld an additional H-pipe in to balance the exhaust,and it will save weight because you only have one muffler hung. Keep in mind that this might affect ground clearance, so do some measuring before you make any decisions. Some people have said that running true duals in a car with few modifictions will actually hurt low-end torque, so read what people reply as I am sure someone will have something to say about this. Other than that, you have the choice of purchasing a pre-fabricated system from either Dynomax or Flowmaster, each of which incorporate a single piece of pipe that attaches where the stock resonator is and uses it's own split and two new mufflers. I personally dislike the Flowmaster system because the tips exit at an angle at the corners of the rear bumper, as opposed to the good-looking (opinion) stock outlets. Anyway, one could write a novel about this, so I will leave you with that. Let me know what you think...
-DG-