you need a high speed dremel tool and small grinding bits. then look at the forum in here on "how to port a nitro engine". also http://www.e-maxximumrc.com/html/nitro_motor_mod.html

theres timing changes beyond whats there, i think you extend the exhaust port up for more top end from motor and you extend the intake ports down for more bottom end torque. also work on the crank. all done in very small increments cause too much = no more motor.