My engine cases were a real mess. Very corroded. I stripped the clear coat off using a spray type I got at Home Depot. Also tried the paste type. It all worked pretty well.
After all clear coat was removed I sanded the pitted surfaces. I started with 1000 grit then went to 1500 and finally 2000. It takes a while to do it this way but it leaves a nice smooth surface. I put the cases on the buffing wheel as the finishing step.
I sprayed them with clear coat (also from Home Depot) to keep the shine. I've read here that some people don't put anything on them after the polish step. When they get a little dull they
just polish them.
BTW, don't try to speed up the job by using a corse sandpaper to start off with. It'll take much more work to polish out the deep scratches ... trust me on this one.