Yeah drop the displacement and weight a little say to 5liters,and remove a few restrictions.5liters with fewer restrictions wont be slow,and call it what it is(which I really dont know what it is-“the sort of resemble a stock car class?”-Kevin
@TwinTubro
GM’s LT1’s smallblock V8’s used cylinder heads based on the SB2 GM NASCAR engine 
The first Harley overhead valve engine was produced in 1936; the 61 cubic inch EL knucklehead (and a hemi design to boot) which is now worth into the 6 figures. It just took the car guys a few years to catch up…
Racing engines in the 1920’s had over-head cams and four valves per cylinder…The alcohol burning Offenhousers were groundbreaking and competitive for decades…The V12 Merlin aircraft engine (1935) was revolutionary for its time…
Motorcycles were using overhead valves after the turn of the century but these were usually the IOE setups; the overhead intake valve which was atmospherically operated over the side exhaust valve.
It was sometime around 1910 that many motorcycles started using a mechanically operated intake valve.
Aircraft and motorcycle engine designers did much of the early pioneering…