Ron, instead of messing about with an original m/cyl, why not use a Brembo? They are available in a range of piston sizes, and body styles, and lever types. Modifying the internals could be dicy safety wise. Better to put the effort into matching levers on a factory part, or chasing down the perfect Jap m/cyl, if you don't like Brembo's.
Frankly, I would put the custom effort into replacing the stock brake rotor with something better.
Also, you don't know how it will feel with the different piston size, and it's a lot easier to swap different cyl assy's to get the correct feel/effect than it is to modify parts. There are a lot of variables that should be considered, besides piston dia. : lever ratio, hose type, pad material, rotor material & surface & diameter & floating/solid, brake switch type, one or two rotors, riding style, riding conditions, fluid, costs, time, etc...
FWIW, I'm speaking from personal experience. A bad combination of brake components put me and my pristine Guzzi BOTT racer shiny side down while braking for turn #4 at Sears Point. it was going to be retired after that race, but I decided since it wasn't perfect anymore, I would continue racing it :lol:
