From the research I've done the new FS entry level engines do have the same block as the more expensive Kawasaki engines found on the JD and commercial mowers. The only difference I saw according to the Kawasaki web page is the carburetors. The FS has a single barrel and the FR has a double barrel carb and a larger air filter.
that doesn't seem right...are you sure? FR is residential model, FS step-up and FX commercial