Scored a used Accufab plenum and throttle body. The plenum has some pitting, worse in some areas than others. I tried some light metal polish but it laughed it off. I did a Google search and came up with a lot of ideas, some contradicting others. The most common idea seems to be start with 200 grit sandpaper used wet, then go to 400, etc. This is a fair weather only car, and under the hood is really nice right now. Any suggestions?