Yes urban 96 is right you are going to need to change the trans, 4.6l and 5.0 runa different set up. The t5 outta a 94 95 car is different from a 87-93. The bellhousing is also different this is because of the lenth of the output shaft to position the shifter in the right spot in the consol. I belive that it is about 1'' longer. You can use a 87-93t5 but it is alot of work. The bell housing is a little harder to find because it was only produces for 2 years.
As for the motor the front cover is the only real difference because of the electric fan, couple other changes like the throttle body, maf stuff like that can be changd though.
I am swaping a 3.8l for a 5.0 but in a 95 car, but i have a wrecked donor car that keeps the cost down, something to concider. sounds like alotta work and if you don't plan on doing it yourself it gunna cost large. Sell the car and buy a new one everyone told me, but i like building them so screw it. Just my 2 cents