Air-cooled aircraft cylinder heads really live a rough extreme hard life during normal operation, especially the exhaust valve components, mostly due to the extreme heating+cooling cycles and full-power continuous running for hours that such an engine must endure. Rarely when a cylinder needs "overhauled" does it have problems with the pistons or rings like in a car engine, but rather it's usually always valve issues instead. So, a top overhaul in an aircraft engine is really more of a glorified valve job than a real overhaul. Getting new piston rings in an overhauled cylinder is icing on the cake since new rings are dirt cheap and even if the piston is not re-useable and must be replaced, the pistons are relatively cheap as well.
The "bottom end" of an air-cooled Lyc is pretty much built like a juggernaut, and if there's no corrosion/pitting of the cam lobes/lifters, then it's not uncommon for the bottom end of an old O-320 or O-360 that has even been run well past the 2000 hour TBO to still look to be in fantastic good shape upon disassembly, however by then every gasket and seam on the whole engine will have been leaking oil like a sieve.