It's interesting that many people don't realize that most "modern" 4 cycle engine technologies like Hemi Heads and DOHCs and rotary valves were long understood many many years ago....the main limiting factor was the lack of supply and refinement of high octane fuels and surfactants/oils to support and sustain the higher RPM and power the engines could produce, and to a lesser extent the metallurgy, casting and forging techniques to mass produce them.....there were some VERY CLEVER ENGINEERS back then.
European companies like Bugatti, BMW and Auto Union were decades ahead of their peers and much of that techhnology and brain trust was diverted toward WW2 aviation starting in the mid 30's....The RAF Spitfire was developed first as a land speed racing plane by a company called Supermarine and converted for Military use.
