An engine builder friend of mine says a 7L V8, turbo charged could easily produce 400Hp for 2000+ hrs. He knows a thing or two as he makes endurance engines in the 2000 Hp range. Now we are talking bespoke blocks and internals, forged H beam rods, etc. Very expensive components. A it heavier than an aero engine......he guesses 10%. Forgings have advanced incredibly in recent years, as has the science of combustion chambers and fuel injection. Interestingly he also says rpm is a big factor. To produce the same Hp, going from 2700 rpm to 5000 rpm actually reduces the stresses on the components. So the V8 is under less stress at 5000 rpm. Cooling (temperature management) is the key to longevity of any reciprocating engine.