In the interest of cleaning things up, I picked up the wire brush pictured. Do I really need to clean all the carbon off the surfaces? It seems to be more "stain" than anything else. Nothing you can feel with a finger.
If the answer is yes, use the brush, do I need to stay away from the valves?
I know from personal experience that that type is not good for aluminum or bronze. I try to use the nylon cup brushes on delicate areas. That said I've never used either on a piston or valves.....yet.
You can see how third generation Model T mechanic Royce Peterson cleaned the carbon from a deck and cylinder head here:
That will not hurt the valves or anything on the top side, actually much easier on the metal than a ro loc disc. KGB
A few more options to consider. One is the Ro-Loc type - sort of a very heavy duty scouring pad. The other 2 are stainless steel braided by Milwaukee. They are marked as being specific for Aluminum and Stainless Steel Surfaces (my head is aluminum Z head).
That all said, I hadn't read carefully and noted James mentioned nylon cup brushes. Not sure if they would get the job done on my head or not, but certainly seem to be pretty safe.
No need to polish, discoloration is no problem. You just want to remove the crusty stuff. Stay away from the course wire wheels on high speed grinder tools. The wire cup on a drill like you shoed should be fine.