Around 02 or 03 they started switching computers to where they need different tone wheels, that requires removing the crank and with the stupid bedplate main bearing set up is a huge pain in the butt. You also have to swap the passenger side cam gear.
I have also heard but never verified it that the motor mount holes on a durango/dakota are in slightly different places than on the jeep.
Ex manifolds are different.
You need to watch for weather you need EGR or not, it is a pain to add it to a non egr engine, you need a real long drill bit that you can control acuretly at a funky angle or you can swap the drivers side head if your old one is still good. If you need it and your donor engine don't have it you can still run the car but you will get a code for it even if you plug in the solonoid and leave it dangling under there. It is pretty easy to block off the passages if your donor has it and you don't need it.
If you have an HO engine you can swap in a non HO and it will run just fine but it will be down around 30 hp. Works the other way also. An HO is easy to identify, there is a big "HO" cast into the head in the valley near the front.
In my experience most of the time it is eaaier to fix whats wrong with you engine than find another, it will soon have the same problems if not addressed anyhow. The most common reasons people come in hear looking for a 4.7 it just needs timing chains, if they drove it far to break the chain it may need some valves replaced and that will also adress another common issue, head gaskets. The head gaskets will blow when it overheats, even a little, heads will also warp a little at that time, if you overheat bad enough they will crack and need replaced, even hotter and it will drop valve seats witch actually becomes cheaper to find a donor motor at that point.
Another common issue where people come in looking for a replacement engine is when a rocker falls off, sounds like hell may be easy to fix in an hour or may screw up the head, pull the valve cover and check before buying an engine.
I have seen only one where the rod bearing took a dump and somehow the crank was still like new, threw a new bearing in it along with head gaskets and timing chains and it is still running good 2 years later.
Unless you got a rod hanging out the side of the block or something I would take a serious look into fixing it instead of replaceing. My recomended updates with an un-touched motor around 150,000 (ironically thats how long chrysler said they would last when they came out with them) would be a complete timing chain and tensioner kit, head gaskets, mill heads, and if you real serious about keeping it a set of valve lash adjusters(they are the thingy that causes rockers to fall off). If you are gonna get a used engine you should doo all this while you have it out anyhow so you might as well just do it to yours if you can.
I am not causing global warming, I am just trying to hold off a impending Ice Age!