The closer you stay to the same generation, the easier it is. 96-99 engine would be pretty close to a drop-in swap for you.
You have to put your sensors into the donor engine. Other things that make a difference are ignition parts, fuel injectors and plumbing, and accessory mounting (esp power steering and tensioner). 96-99 is mechanically the same but some of the other stuff might still need to be swapped.