Re: 5.0 EFI Good/bad years??
You'll want an 89-93 mass air fuel injection system. Prior to 89 most, but not all, Ford EFI systems were speed density. SD systems are not very modification friendly. Post-93 systems are mass air systems but they are also On Board Diagnostic II systems (OBD II). OBD II system EEC's are programmed to monitor various parameters of the engine and the EEC "expects" that these parameters to stay within certain limits. Therefore, OBD II systems are not as modification friendly as the somewhat simpler OBD I system of the 89-93 EEC's.
A good book to read for the scoop on Ford EFI systems, how they work, how to tune them, how to modify them, etc., is "Ford Fuel Injection & Electronic Engine Control" (89-93) by Charles O. Probst. Amazon.com sells it for ~$20.