Some ppl say the torque rating on the T5 that comes with the V6 is not as strong as the T-45/T-3650 that came with the 4.6's, but depending on the year I think the T-5 is rated at 300 ft/lbs. You would most likely need the correct bellhousing and flywheel though from a 4.6 Trans. You can probably use the bellhousing, but I would think you would need a flywheel to balance the motor correctly and to ensure that the starter will engage correctly. I don't have the specifics on the parts you need, but those would be a good starting area. The T-45/T-3650 that came in the 99-04 GTs are rated at 325 fl/lbs torque.
2002 True Blue V6 to GT Vert
16.1@86 as an auto 3.8
2.15 60', 9.3@77, 14.4@96 as a 5spd SOHC 4.6