Hope with @k_vanlooken’s help it is now possible for everybody to download the book. Thanks so much Koen for sharing and dividing it into smaller bits!
Well, flat head engines were very commons those days. They wrote that a more compact and less rugged cylinder head is better. This is often better achieved with OHV, but can’t generalized. It is more depending on the actual design of the engine (valves, inlet and exhaust) than on OHV or flathead
Also, it is with some flat head designs not easy to increase the compression ratio.
Remember, this is technical state of the 40s.