Do you have a wiring harness, ecc, and exhaust for the 5.0?
To take out the 3.8 you unbolt the tranny, unbolt the exhaust stuff and remove it, unbolt the 4(?) engine mount bolts then disconnect all the vacuum lines and wiring and such and label which vacuum hose does what and so on and so forth.
There could be more but that's the basic jest of it.
I would suggest getting a 8.8 rear end as well. The 7.5 won't take a whole lot of abuse from the 5.0.