Depending on your wrenching skills, should be "relatively easy". Miles ahead with a complete doner truck.
Off the top of my head, and others will undoubtedly chime in.
You are going from a v6 tbi to a v8 vortec. So for suren engine mounts and fuel pump. Then all the wiring for the v8 including the computer. Computer would probably have to be flashed to remove the VATS. All the cooling system components including rad and shroud would definitely help.
What trans are you planning on running?
May have to deal with driveshaft being different depending on can and box length.
If it was me, I would park them side by side of possible, and remove the v6 and it's wiring harnesses. The mounts have to be swapped to the v8s. Then remove v8 and V8 and reinstall it reversed of how it came out. Lots of labels on wires, pics as well. May have to some rework to the wire harness.
It's been done before, a bit of searching on this site should find you a thread or 2 for sure.
Good luck, and keep asking questions, and someone will probably have answers.