"Flathead" Ford engines had the valves in the block, not the cylinder heads. "Relieving" the surface of the block between the valves and the edge of the cylinder by grinding away a little metal increased gas flow. So did "porting and polishing"- - - -grinding the intake and exhaust ports bigger and polishing the surface of the cast iron to make it slicker and reduce turbulence. I did all of that to my first car, a 1947 Mercury convertible with a bored and stroked and ported and relieved flathead V8 engine with tubular steel headers and Offenhauser finned aluminum cylinder heads.
Sometimes complimented by milling the heads a few thou to increase compression.
