I would be more concerned with a leakdown test and a oil pressure reading. If you have minimal leakdown, both rings and valves should be in reasonable condition, and would have a remaining working lifespan related to how well they currently seal. The oil pressure should give an indication of the rod and main bearings. If the oil pressure takes longer to build, and drops off instantly when the engine is shut down, one can reasonably infer that the clearances are more open than a similar result where the oil pressure came up instantly on start, and took a few seconds to bleed down when the engine was stopped.
Listening for internal engine sounds can also give an indication.
My take on service life is that the results are totally based on service done and how the engine was used. Engines that are started and put to work without a few seconds warm-up will generally last a shorter time than those that are given a bit of warm-up time. Generators seem to be the most severe conditions, where they are expected to start cold, and run to full speed within seconds. In those cases, lubrication is likely not well supplied though modern oil will minimize the lack. Oil and filter change intervals, and whether the oil was left to the point all additive packages were worn out also affects longevity.
If you can inspect the equipment at the same time, it might give an indication of the general care given. Rusted and dented equipment generally indicates it was driven and use like it was stolen... i.e., run hard and put away wet, never given reasonable service. The other end of the scale, where equipment is not in poor condition generally indicates at least some service. And best would be talking to a maintenance crew to see if they have an idea of the service provided.
So, IMO, hours of use can indicate something, but are not an absolute measure. FWIW.
tom
