I'm no guru, but since noone else's chimed in.
First off, a couple of questions.
Did you just get the motor? Or the Motor and trans?
What tranny's the 4cyl got in it right now?
Are you looking to go EFI or carbed?
Some basic stuff you need to know: (I'm sure some of the more knowlegable folks can fill in anything I miss.)
Swapping a 5.0 for a 4 cyl is completly do-able, but its not just the engine you've got to plan for.
Trans: If you've got the 4cyl t-5 in the car, its not as strong, and IIRC has a different input shaft depth (?). AOD/e, I dont know if its the same tranny or not.
Brain: If you're going efi, you'll need the computer and harness from the donor car, and make sure its for the same tranny type, i.e.manual comp for a manual tranny.
Thats just a start, but if you search the site for 4 cyl conversion, you'll find pleanty more.
Hope it helps,
J