So let me get this straight. You screwed up an intake manifold swap, left a sensor out without even knowing what it was, ran the car with no functioning cooling fan because of that, and overheated a 4.6 enough to blow head gaskets on one of the most indestructible engines ever to be put in an automobile, and now that you have completely failed at such a menial task as an intake swap, you want advice about swapping to an entirely different engine? My advice would be either find a reputable mechanic and pay them to do the work for you, or forget the T-bird and go lease a Camry. You clearly are not up to the challenge of this swap, and any attempt you make will only make your situation worse.