4x4 Frame swap

I have a 2wd 2004 sport trac, a 4x4 sport trac has come on sale near me for fairly cheap due to it having a bad engine. My question is how difficult would it be to put the body of my truck onto the 4x4 frame and put my engine in it. Keep in mind that I do have access to engine hoist and a lift. What are some difficulties or challenges that I might encounter when doing this?

I’ll be interested in how that goes. If you pull it off you are a better man than I.

It's a MAMMOTH job!
You need a lift or 2 gantries, so you can lift the body while you slide out one frame and slip in the other one underneath.
Or else you need at least 4 strong men to lift the cab and someone else to put props under it (like beams that you set on top of pedestals).
Then you need another big double-bay to set both frames side-by-side so you can do the swap of all parts/components.
It's a gigantic job.
I was a mechanic in the 80's and 90's and did pretty much anything on smaller vehicles.
We had all the equipment and routines to get the jobs done.
We did framework, engine swaps, tranny jobs/clutches, unibody work, prep and paint, you name it, we did it (all except engine rebuilding that required a machine shop).
If you take-on this project, make sure you have at least 2 weeks for steady work on the project.
If you can lift the bodies off (the bed is pretty simple) and set them aside, then that's the biggest hurdle.
But once they're off, all the work is in the swapping.
I have a very rusty 2003 XLT that I was toying with the idea of doing a frame swap.
But upon reconsideration, it seems like too big a job for my age and resources.
It's a hard pill to swallow, since I took very good care of this sport trac.
It was the 'liquid salt' in Detroit that killed the frame.
And for some reason, the fools at the stealership 'forgot' to undercoat the frame, which was pre-paid at the sale.
Oh, and don't let me forget all the money you're gonna want to spend on all the essential maintenance and repairs when you have the body off.
You may run into body rust or other issues with the body or 'new' frame (like not so clean cross-members, shackles, etc.).
You may also want to do a timing chain on your engine, and do all the intake manifold seals, swap the plastic thermostat housing for an aluminum one, etc.
There are many things you can do to your ride to make it more reliable while doing the swap.
All of them cost $.
The prices of parts these days is extortion, so be prepared to PAY.
Anyway, good luck w/your project, if you decide to do it!

Exactly what @cadman777 said. I've done a body swap on a Nissan Hardbody, regular cab to King Cab. It is straight forward but a lot of work. I would say you would need more than 4 people if that is the way you would go. I did it with 3 people and the cabs were stripped. no interior, no glass, no doors, no wiring, no fenders, stripped.

And what's crazy is Ive seen the ST body's hanging from trees on the forum back in the day, It can be done, Biggest problem will be broken bolts, Rusted parts and connectors or wires that chafe....