Recently, I used these 3M 3" discs to polish up some aluminum and they worked great. I bought a combo kit that had 1,000-5,000 grit discs.
They chuck up in a drill using a 3M rubber backer. All I used was water throughout the entire process. Next time, I would use some polishing rouge as well.
For heads, this would be ideal unless you want to get in between the fins.
This isn't the combo kit I bought, but it's the same product.
https://www.detailing.com/store/3m-p...box-of-50.html