An exhaust shop could modify that, no problem. With what you are proposing, a trip to an exhaust shop is mandatory, unless you weld.
Nothing about 2 into 1, back into 2 screams horsepower increase. Unless you run at least a single 3" pipe back to dual pipes at the rear.
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