Removal of lead, and reduction of sulfur from the fuel helped tremendously.

Finite element modeling of the engine structure and cooling system reduce assembly and operational distortion which reduces wear.

Ever look at how the head bolts are designed on a modern engine? they no longer are threaded to the top deck, but rather are long with counterbores to reduce bore and deck distortion.

Thermal modeling of pistons, valve bridges, and cooling systems is s.o.p now

Computer modeling capability wasn't available in the 50s and 60s. There was a lot of trial and error engineering back in the day.