2001 Ford Explorer 4.0 timing chains

I have a2001 Sport Trac with a 4.0. The timing tensioners went and a rocker dislodged. I need a new motor. I cant see putting a used 2001 4.0 in due to their problem with tensioners. I have found a low mileage 2003 4.0. The book states that I cannot swap them. I do not believe this. Why? What needs to swapped out from my 2001? A rebuilt motor is too much money right now. My build date is 9/2000.