If you find a 5.8 from a 91-94 truck or bronco that had a E40D in it then, you can use the ECM, wiring harness and everything would be relatively straight forward as long as you kept the speed density system. You will run into issues once you do the MAF conversion. The reason I suggested the 95-96 donor vehicle is because that was when Ford actually put MAF on the truck from the factory and it would be a lot easier with that vehicle. If you make the swap to the 5.8 speed density and then want to convert to mass air, you will need the following things.
1. ECM from a 95-96 Bronco/F150 with E40D transmission.
2. Throttle body to mass air meter Y duct (F5TZ-9B659-F) K&N makes one too.
3. Mass air meter housing and sensor that is calibrated for your engine injectors.
4. Mass air meter sensor wiring connector
5. Second oxygen sensor for the "left" side of the vehicle. (Alternately you can split the signal from the single sensor but that's not a long term solution)
6. Do research on the sites below that will help you determine the differences in the wiring harness of a speed density truck and a MAF truck. I personally got a harness from an 89 mustang.
OldFuelInjection.com is an absolutely awesome website that has a lot of valuable information.
Another good site for 5.0 but I'm not sure about the 5.8
I did my conversion somewhat differently from this guy but it gives you an idea of what is involved.
As far as wiring, know that the injector wiring will completely change. You will add the MAF sensor as well as an O2 sensor. Make sure you have quite a bit of patience and a little determination.
If I can help more, please let me know.