Im surprised no-one has really mentioned head work...the factory 25de ports are fkn shit...and give next to no swirl in the combustion chamber...which means upping the compession much more than standard is going to mean bulk det with any meaninful timing advances.
It wouldnt be hard to raise and reshape the ports to give a better entry angle to the chambers, Also Long runner ITB's will help high rpm cylinder filling, short ones might mean the engine will free rev quicker but wont help power or torque on a small motor.
And on a short stroke motor short large diameter exhaust runners should help with high rpm breathing.
Then get cams made to suit, and rev to 9000+
As others have said aiming for 100hp/l will mean it wont be much fun at low revs/street speeds, but find a set of 4.7:1 r200 diff gears and rev the crap out of the thing.