I tried different polishes on my stock cans and have polished the Holeshots twice. As someone else said, unlike aluminum, they don't hold the lustre. It seems like a weeks worth of heat cycles and they regress to about the shine they had out of the box.
I polished my stock cans twice, by hand, using some stuff I got from the Autorama...man, they came out shiny, with bluish tint, rather than the yellowish tint the header will get, and were gorgeous. Alas, it doesn't stay.