Those upper rails probably have less than 100k on them. Thye are only half way to the darkness that is disaster. Those rails have nothing to do with the length of the chain though as they do not touch the chain when it is tight.

It is hard to tell about the extent the tentioner is out though with pictures, maybe even in real life. I usually depress the tentioner to release the oil and then see how far it must extend to hit the chain. It is still ambiguous. I'd just put new upper rails in and leave the rest. The chains never fail on their own and replcing it won't help the lower rail if it is about to wear through.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician