What is a Flathead? It is a valve in block engine. As you can see, the valves are in the block next to the cylinder bore. The valves open into part of the combustion chamber that is next to, rather than directly above, the piston. If you look at the engine with the heads removed, you will see the top of both the intake and the exhaust valves, and the top of the piston.
What are those numbers? Go check out how to hot rod the flathead.