Well funny you should ask..
I sanded it flat with 200 grit, then 400, then a wet sand with 1200 to remove the brushed finish that Doc painstakingly created. After that i moved onto a cloth buffing wheel on a drill with a bit of Autosol metal polish.
I also tried a dual action orbital sander with foam and wool pads with a variety of cutting compounds (normally used for car paintwork), and i found the Autosol and buffing wheel worked the best. The surface will never be a perfect mirror as there will always be micro scratches that you will see when viewed at certain angles, its not a true mirror or chrome finish, its just highly polished metal. That said i am really happy with the finish as the reflections are nice and clear and crisp.
I tried two different types of clear coat and neither of them would take to the surface properly as they just cant grip onto the surface. In both cases i was able to scrape the coating off using my finger nail so i gave up in the end and just left it bare.
Only thing to keep in mind the metal is soft and easily scratched so you have to be mindful about what you use to polish out the finger prints, which brings me onto another point, its best avoided if you suffer from any form of OCD
The photo was taken just after i finished assembling the Crack so the surface is covered in grubby finger prints, beauty shots to follow shortly...