Stocks opened narrowly mixed in higher trade Monday, echoing action in overseas markets and little affected by a gain in manufacturing activity in March. The S&P 500 warmed 0.2%, the Nasdaq 0.1%. The Dow Jones industrial average eased 0.1%. Volume rose 14% on the Nasdaq, where trading in Express Scripts (ESRX) was running more than 10 times its average. NYSE volume rose about 8% compared with the same time Friday. The Institute for Supply