Yes it is a large case Fox engine. It is a .45 displacement from the marking on it too. The spinner backplate is actually integral with the drive washer so that it is the drive washer and the spinner backplate too. If I remember it was the deluxe version of the engine.
The easiest way to tell is that the small case .40 engines have a plug in carb that plugs into a socket or hole in the crankcase.
The big case engines use a flange mount carb that mounts on a flat flange on the crankcase.
Obviously, if you see the two sizes of engines side by side it is really noticeable too. The small case engine is really small in comparison.