Sounds complicated. Personally, I would get and install the full mandrel bendz 2.25 kit, and put an x-pipe resonator where your y-pipe is, and two 2 1/4" mufflers in the stock location.
But if you're set on a single exhaust, definitely a 2 1/2" pipe and muffler (ditch the 2.25" muffler). That's not much of an upgrade over stock as the mid-pipe is 2 3/8" from the factory.
97 T-Bird LX 4.6 - 80k miles
94 Supra TT Auto - street/strip car
04 CVPI- Brenda's car - 76k miles
95 T-Bird LX 4.6 - fully optioned, owned 15 years, 220k miles
96 Cougar XR-7 4.6- Brenda's car, owned 11 years, 187k miles
88 T-Bird 3.8 - first T-Bird, owned 5 years, 206k miles