Hey
I did something similar I swapped an 03 escape seat (headrest) into a 98 explorer. The easiest way was to use the slider mechanism from the 98 and bolt it to the 03 seat. This is that hard part, you can drill holes for bolts to bolt the two pieces together or if you have a welder just weld a threaded rod where the bolt holes on the slider mechanism rest on the seat. Cant tell you if the 3rd gen seat has the same mounting stuff as the second though.
-Jake