I have 2 carbed 5.0's and the efi 2.3 I just got. I built the 82 5.0 rom a straight 6 car about 5 years ago.
Given the price of gas, I would keep the four, as that's why I got one, and am busting my tail to fix it up. The price on these puppies is going to go up shortly. As you know from finding this forum, all the non engine stuff from a 5.0 to a 2.3 Mustang is the same, so you can build the rest of the car easily. The 2.3 is an excellent engine in my opinion, and worth keeping. It is relatively straghtforward to work on and repair. Looks like a couple of seals would fix yours.
The 2.3 to 5.0 conversion is very common, but used 5.0's are inexpensive enough that I would not want to go through it unless everything was dirt cheap, or I was building a hot rod. You need so much stuff off the 5.0 car that is Mustang specific that you would have to buy a wrecked or ragged out one anyway. As others have said, you need the wiring harness and sensors, the computer, the engine and accessory brackets, cables, the trans, driveshaft, etc. Some fuel tank work is needed. Nice thing, is that it all does fit, and work.
You could swap using the Lincoln computer, but you will not end up with as good a conversion as using a Mustang. The Lincoln engine may or may not be a 5.0 HO. Someone else here on the 5.0 tech forum could tell you.
And, yes, this is a more appropriate question on our 5.0 board.