I wouldn't soak in acetone. Perhaps a test--put some acetone on a rag and rub a small spot. If the acetone is going to take off this paint it should happen fast, so soaking and possibly softening the whole cowling shouldn't be necessary. Sanding with a coarse sandpaper will probably work, as well. But that'll take a lot of elbow grease and then repeated sandings with increasingly fine sandpaper to get all of the scratches out. I'd try the brake fluid first. I don't think it will harm anything.