Freightliner

Hello to all, I'm new to this site but I just bought a 2000 discovery 2. It has a noisy tappet problem as well that gets louder upon warm up. It's a 4 ltr engine and I would like to repair it myself but I'm new to the landy world and I'm just learning about them. Now as I've been told the intake and all has to come off to do the job. Any info that anyone could offer as where to find a manual or what all is involved would sure help out. Thanks