[noahsdad]

Your biggest problem with any swap is going to be the computers. Because your Seville is integrated so tightly through several systems, the ECM, BCM, OBD, Programmer and the Climate Control Panel, stepping outside the 4.X engine realm is more challenge than it's worth, unless you're also planning on doing a custom dash. The 4.5 is the easiest swap, but still requires a fuel pressure regulator and a bit of tweaking to make it reliable.