I am also confused.
The speedometer hooks via speedo cable and gear to the trans....no electronics.
Now, if the car has a late model 5.0 in it, there is nothing to hook up from the engine other than:
-oil sending unit
-water temperature sensor
Those two items hook up nearly univerasally on Ford engines prior to 1995.
What else needs to be hooked up? Please be specific as there are not many things, if anything, that are engine dependant that need to be hooked up.
Was this car running and functional when you bought it?