oops I messed up when I said that head bolts don't need any sealant, they definitely do, but not RTV lol my bad
and well you can never judge an engine by the mileage. theres definitely some better running 250,xxx miles engines out there then some 50,xxx mile engines. just depends how it was treated and maintained. and also on whose working on it and why.
for instance my dad bought a 78 chevy 3/4 with 55,xxx miles, but what do'ya know, it's a sledge monster and I killed the engine from alot of highway driving
it was the original old man who owned it, but what happened was he only really drove the truck to work and his work was so close to home the engine never got wormed enough to keep it flowing good and clean.