My Dad's 01 v6 regular cab bit the dust 364000 miles. He bought a 5.4 from a wrecked 02. Will he need to do front end work? Replace the springs? Who has done the swap?

 

He will need to ======
Replace the complete engine harness,
Replace the PCM,
Reflash the PCM to get the dash and Pats to work,
Replace the radiator,
Replace the exhaust plus all the little things he runs into.
Are you sure he would want to do all that rather than get another truck and eliminate all the hassle?
Good luck.

 

Yea....I would not do it. He is bent on doing the swap though
What are "Pats"?

 

This is indicative of not knowing much about the trucks over the years until he wants to do this.
PATS is the anti theft system and electronic dash that works with the PCM on a code basis. No two codes are the same so it has to be done.
This is where the re flashing of the system comes in when trying to use the 5.4 PCM in a different truck. It should work if re programmed by a dealer.
If he won't listen, then he will get to a point where he is stuck unless he does these things. If not, then the time and expense is all lost and a truck that cannot be used or sold for anything but parts.
If the donner truck is repairable, that's the route to take. It is a lot less hassle and nothing to figure out or swap and re program..
Good luck.