I managed to prep a valve cover for paint/POR-15 in a floor standing sand blast cabinet. It made all kinds of funny sparks when the abrasive hit the chrome but the fairly fine abrasive left just enough key to make a good bond, no distortion that I could see took place. It was more a surface roughening than a material removal. Perhaps try your abrasive of choice on a scrap of something of similar weight before your valve cover?
