Here's the deal, the gasket doesn't care how shiny the surface is, all you need is smooth, and more importantly, parallel and flat. If you can't feel it with a fingernail, you don't need to worry about it, it won't affect the seal. Anything more is a waste of time, and quite possibly a detriment to the seal, polishing gasket surfaces can cause gaskets to creep out under pressure, as can putting rtv on gaskets that were meant to be installed dry. Abrasives are a no no, due to potential internal damage to the motor, steel doesn't mind wire wheels, as long as you don't go overboard and try for a mirror finish, but aluminum is softer, and the risk of removing metal is very real, in fact, it's likely. On an old small block Chevy and the like, the tolerances are loose enough, and the gaskets are thick enough, that people have been getting away with bad practices for decades. Modern motors... not so much. When the roloc discs came out, we thought they were heaven sent, then we stared getting bottom end failures soon after top end jobs, the mfgs did a little digging and found out that the silicon abrasive from the discs was causing bearing failure, and more importantly, that the particles were too small for the filter to catch. A gift that keeps on giving. I realise that everyone's dad did it that way, and it always worked, hell, I did it that way for decades, but getting your twinky slammed by the warranty police will get your attention fast, I'm a believer now, and my shop follows the new rules, and guess what, we don't get repeat failures. It even works on old motors, my 912 motor is dry as a bone on the outside, even the Nash Metropolitan motor doesn't leak much.
