Do not waste your time or money on compression tests or timing chain chain replacement.
The best preventative measures in this instance is to use a good quality engine oil and service regularly, together with very regular dip stick checks on the engine oil level.
At 135k miles there is bound to be wear and tear present, so chains and low compression issues should only be dealt with as and when they happen, which might be never.
However, if the engine eventually does go pop, then just drop in a known pre-owned engine from a known and reputable seller.