Hi
In the moped transfer porting I have bought small grinding stones (general use not any special, they are chinese and soft but they are for only one use)and put on an electric drill, better of high speed, this must be in the hardware shop and are cheap , and with patience I modified, the material was iron but soft, I believe the aluminium is easy to grind.
Put a mark with permanent ink marker , it is the limit of grind work.
Be careful do not touch the cylinder surface.
If you have a friend with a Dremel better, but with care you can make with electric drill.
Have fun .
Jose