Mill head .050" , install some honda valves with split keepers, 5mm valve guides , longer push rods and adjust height of rocker arms to keep valve train geometry in check , port and polish head, get a cam from AGK and curved manifold , 19mm carb. and filter , header,advance timing. These engines will make 6hp or more with these mods. and turn 7000 rpm without billet rod or flywheel all day long.
Done it !!!