This is an axial or barrel engine, which has multiple cylinders arranged around and parallel to a central shaft, like the chambers in the cylinder of a revolver. The piston thrust is converted to rotary motion by a swashplate, wobble-plate or Z-crank mechanism.
This is a Curtiss OX-5 "Hemmi" cross-flow head engine built in 1918. And looks like pushrod and rocker exhaust with pull-open tube and lever intake. With the pushrod running inside the tube. I'd love to see the valve train at the camshaft.