The house I lived in and the food I ate in the 1950's and 60's was paid for by my father keeping these old cars and trucks running. The average stovebolt engine back then needed a valve job about every 30K miles, usually got its first "in the frame overhaul" (piston rings, adjust the bearing clearance, and maybe a second valve job) at around 50K, and if it managed to make it to 75K it was time to pull the engine, rebore the cylinders, regrind the crankshaft, install rings, rod and main bearings and grind the valves again. Valve guides, cam and lifters, and a few other long-life parts might get replaced, of maybe not, depending on how well preventive maintenance was done.
When PCV ventilation systems became popular and/or required to meet air pollution standards in the late 1960's, an added benefit was an approximate doubling of expected engine life because dust and dirt contamination of the crankcase got drastically reduced by the closed ventilation system and the elimination of the road draft tube.
The old adage I heard a lot was "A Ford breaks down- - - - a Chevy wears out!" That was particularly true about transmissions and rear ends.
Jerry
