It would be far cheaper to get the 5.4L to work than a 5.0L. Aside from a ECU reflash the 5.4L is more or less a bolt in, as close to one as you can get these days. You could run it off all the 4.6L wiring. It would be easier to go to a NPI because of some sensors the PI would have but really nothing major compared to trying to get a 302 to work.