Few large traders of credit-default swaps would get hit by new tough rules governing the derivatives market if draft proposals issued by federal securities regulators are adopted. Securities and Exchange Commission staff said no more than about 10 firms that aren’t derivatives dealers are likely to be deemed risky enough to require heavy federal oversight. Officials said the SEC hasn’t yet ascertained which firms those might be. The SEC proposed setting high thresholds for a trader’s market exposure so regulators could focus on the riskiest players, an agency official said.