The dremel will be ideal. Use 1/8 aluminium cutters like these
Attachment 55Attachment 56
should be able to get them from bunnings. Use your stones on the guide, and 60 grit sanding rolls for the rest. Most of your work will be done with the sanding rolls. Shaping and tidying the port. Bunnings sells dremels with the extension handpiece for a little over $100. The extender makes it real easy to use. If you have this you'll be laughing.