Nope. Won't work. Like the T-45 and T-3650, the T-56 has an integrated bellhousing.
That means for each vehicle, the car has a different bellhousing bolt pattern.
On the Ford's, the T-56 will only bolt up to the modular engine platform.
There are kits to make it work with the 302 and 351, however i doubt they exist for the 3.8L
But a 6-spd with a stockish 3.8L is useless. The engine does not have the power to make use of the 2.66 1st gear ratio unless you have 4.56's or 5.10's out back in the rear. In reality it would make the V6 slower. It makes stock GT's a tenth or two slower.
Think about the cars that come with T-56's factory. GTO's, LS1 trans ams and camaros, Z06's, Vipers, CObras....all with gobs and gobs of torque. The gear ratios are optimized for them.
The V6 has a T-5, which has not been used in a V8 Mustang since 1995.