Yeah, that would be a helluva lot of work for not much gains. Just buy a Mazda6. I know I'm planning on it.
BTW, the 2.3L duratec is REALLY different. The intakes is on the front of the engine, it has coil-on-plug ignition, and MANY other changes. It also can have the 4F27E tranny bolted to it. Both Lentech and CP-E can bulletproof it.