One thing you must note about my timing chain recommendations. I am a firm believer that the rails do all the damage. I believe that periodically the chain tentioner will bleed down no matter how new. The real preventive maintenance is to replace the rails before they turn brittle. This happens with age and mileage. I would do just the rails every 75k or 5 years. They are cheap around $3 a piece (three of them). They do require a piece of labor as everything must be removed from the front of each head (alt, P/S).
Bosch Master, ASE Master, L1
33 years MB technician