Care to prevent gouging metal and any method should work. So take your time. Just keep the scraping tool edge parallel to the work surface so the scraping tool corners do not get a chance to dig into the part surface to prevent making gouges. Also keep the angle of the scraper low to the work surface to have better control.
Wire wheel in hand drill, scotch pad in a hand drill are other options. As well as a single edge razor blade, sand paper on a sanding block, and spray on gasket remover that helps to soften up the old gasket and makes it easier to scrape off.
