Actually, i'm goin' thru this right now!
Info on the engine is incorrect, you can use any 5.4 from a truck or expedition from 1999 to 2003 (P.I) engines so long as you stay with a 2V engine, or 1997,1998 (non-P.I.) , but they are less power.
Can't quote exactly when, but the Navigator's got the 3V engine sooner than the Expedition, possibly in 01' i think.?
But as far as the Expedition goes, the 2v engine ran from 1997-2003.
Hope this helps, and i used car-part.com to get my new engine as well, it's a great site if know what u need!