I have used many of the above methods. I have found that the oven cleaners work great on cast iron but too tough on aluminum. Shot blasting gives a nice look but don't sand blast. For some reason, the sand blast gives a more undesireable look (dull) than actual shot. Also, more recent (new) shot is a better choice. I have painted an intake with the clear engine enamel and after it got hot, it turned a yellow color.