It Can be done, but you have to bear in mind your gonna have to chuck a lot of money at it....
i've been toying with it as i have a spare engine and being a motorcycle mechanic, can do alot of things myself.
Looking at major engine and fuelling tuning, based on the weight loss, and the power gains, i dont see why my bike shouldnt be able to produce 22.5VBHP.
although once im going to bore it out to from 48mm bore to a 52mm (anymore than this you will go into a water jacket! and just for sh*ts and giggles whack some Hi comps in,
The major "restrictions" are Exhaust headers, airbox and fuelling,
the exhaust headers have a core tube restriction in the front header and a manifold and pipe decrease on the rear (ever notice the different sizes between the 2 pipes?)
the front header has a O/D of 36mm with a wall thickness of about 1.5mm and the rear has a O/D of 25mm with same wall thickness.
the reason for this is basically honda being smart and using backpressure to basically restrict the motor by its self as the front cylinder with get slowed by the rear, because of the effort to push gases through a smaller diameter pipe. (blow through a calypso drink straw then through a normal one, same principle)
end result and thats including new camshafts,free flow filter,Jet kit, the bore out, high comps and maybe a thinner Head gasket and all the other add ons and there is a possibility of "achieving" 25-28BHP.
I'm only doing it as it makes it more different, yes you could try and slot a different engine in, but wheres the fun in it? ;)