While there have been metallurgy improvements and possibly improvements in manufacturing and oiling the same basic design is still being used, even I dare say in the latest V8 OHV engines from GM, Ford, Chrysler/Dodge.
Have to say it works pretty darn good though of course the rev limit is a bit low compared to OHC engines. My GTO's 6.0l V8 OHV engine was limited to IIRC 6K RPMs (and so was my Camaro Z28's 5.7l V8 and even, and this is a bit of a contradiction, my Mustang GT's 4.6l SOHC) while of course my 2.7l Boxster engine can go a bit over 7K RPMs.