This engine is from Sterling Engines of Buffalo NY, maker of gasoline and diesel engines for marine and industrial engines during the first half of the 20th Century. The 1938 ad shows one of their more unusual products.
This horizontally opposed four cylinder two stroke diesel has two pistons per cylinder acting on a common combustion chamber. Instead of the usual rods and crankshaft,the pistons forces act against inclined discs located on a main shaft.
Above; the main frame of the engine with the main shaft and power discs in place.
Below; Main working parts of the engine showing the framework carrying the guide rods.