There a guy around here who was running a all motor D16Y8, that made a little over 180hp to the wheels, and was daily driving it on 91 octane. I am not sure what he had in terms of internals, but I am sure 200WHP on an SOHC motor is obtainable.
In fact I bet you could do it with D series pistons, as there are some crazy D series pistons out there like the GX and D16A9 pistons.