You can polish calipers. It's doable for sure. But if you are doing it by hand, it's going to take probably 5-6 hours per caliper. Then add how much time it will take to take off the calipers, rebuild them when you are done, and put it back on. The reason i suggest rebuilding them is you will get alot of dust in them, and the dust is aluminum so your piston could easily sieze. And i probably wouldn't recommend regular off the shelf clearcoat on polished aluminum. It can look really bad. I'd powdercoat them instead. So unless you plan on buying an extra set, i don't really recommend it.