Neil, actually your about a decade late in that description...
The early fifties at the Brickyard,,, Indy...had the offenhouser..... and the winner at Lemans about 1952 ( I think ) was an XK 120 Jag 6 cyl double overhead cams....
The Chrysler Hemi I was referring to was started about 1954 and was at 392 inches by 1957....
However, you could make a double overhead cam, crossflow hemi head engine with very modest output if you do not make the cam lobe design of sufficient overlap... ( meaning that the exhaust and intake valves are open at the same time to do as complete a job of getting the burned mixture out before closing the system to start the compression for the next stroke )...and duration...and lift....
Lotus's engine would not have been a ball of fire if they had kept Uncle Henry's same cam lobe specs...