[special-K]

I know there's a thread on cleaning. I just read it. But,that's minor compared to mine and my request would not be seen by all those who already saw how that thread went.
I got these 9.75 x 16.5 aluminum slots (no clear) that were about black when I got them. I cleaned the front of the two better ones pretty good,but the backs and slot holes were still but fugly. So,I decided it was necessary to start from scratch. Maybe I effed up,but I used over cleaner on the backs. They're all white and crusty now and it streaked the fronts that I had cleaned up (I knew I'd have to go back on them). The backs are too difficult to sand. I'm thinking bead-blasting is my only choice now. Agree? Just the backs? The fronts have dark streaks that would sand out,right?,but just need to start more coarse like maybe 220. I was using 400 and nit getting very far with it. Even the black ones (I assume left on the front a long time) I think will sand out. I have to do the backs and slots before worrying about the fronts,I know that. Any advise would be appreciated. I'll grab pictures,but in the meantime I wanted to get some wheels turning (no pun...well,maybe a little)