I don't know what smog laws are like in Iowa but here in California it took six visits to the smog referee to validate the 5.0 EFI setup in my 84 SVO. A dual exhaust just fit into mine but that's something else you have to consider. If you are really set to do this then PM me and I can give you more details.
Also, the rear end is different. The non 5.0 use the 7.5 while the 5.0 uses the 8.8. And I think that the trans mount is different. The 5.0 has a double hump for duel exhaust. I know that the earlier FOX Mustangs has a difference. The drag racers like the softer front springs but would not be good for the street. IMHO, if you looking for a streetcar then it is a lot of work. If you looking to build an SCCA AS class race car or Drag racer and you got a great price, then not a bad place to start. Good luck
Lot of good stuff mentioned so far. I'll add a little.
A lot of people (including me) don't worry about the rear end unless you're dragracing. Run it 'til it gets tired, then worry about putting in an 8.8"
If you're lazy and cheap (who, me?) you can swap in a carbureted 302 with Duraspark ignition, or MSD, or etc. Don't even bother with all the computer stuff. It's easily done and all your guages are not related to the computer harness. You will have to use a fuel pressure regulator because the in-tank pump puts out way too much pressure for a carb. A better idea might be to swap in the tank unit from an early 80's Mustang and then run any fuel pump you want.
Lots ways to swap to a 5.0. The very best way would to have a wrecked '91 5.0 car side by side with your 2.3 car. The other options require quite a bit of work and junkyard scrounging. Check out your local inspection/emission requirements first. You wouldn't want to build a car you can't license.