I look at the spark plugs to see if the engine is worth buying. If the plugs are nice and clean the engine should be ok.
You could do a compression test also.
As far as the actual swap.....................
You will have to remove the motor mounts to lower the engine so you can access the engine bolts to the tranny. Unbolt the mounts from the engine and frame, don't take out that big bolt that's in the middle of the mount. Be sure to support the engine.
There is also the "shock" (sorry don't know the correct name) on the front suspension, it sits sideways under the front of the engine. I had to unbolt one end and move it for clearance.
Another thing that is good to do it very clearly mark the position of the flywheel/flex plate in relation to the engine before you pull the engine. I used some spray paint once all the bolts to the torque converter were removed. The holes in the flex plate will give you a near perfect mark. If you don't mark this it will be tough getting it all lined up later.
It would also be good to remove the grill, but I got mine in and out with the grill in place, but it's real close. lol
I removed my intake and exaust manifolds from the engine but left the head on.
It will take some raising and lowering to get everything unbolted, also probably a bit of cussing.
I got mine out by myself, but needed someone to help getting it to drop in correctly.
Have fun and be careful, it's a lot bigger than it looks.