There is no need to replace the valve guides or seals unless the engine is using oil. They are not a preventive maintenance item.
These engines have a ratcheting tensioner, so it does not need to be replaced on a periodic basis. The ratcheting tensioner is the saving grace for the chain itself, so you do not need to replace the chain until the engine comes apart for some other reason.
My M103 engine now has 240,000 miles and is going very strong. With frequent oil changes, and a little luck, the sky is the mileage limit for these engines.