The Federal Reserve's board of governors approved a plan for Security Pacific Corp. to acquire American Asian Bancorp and its subsidiary. Both banks are based in Los Angeles . . . In a Securities and Exchange Commission filing, Orion Capital Corp. said it raised its stake in Los Angeles-based Postal Instant Press to 12.7% of the common shares outstanding and may increase it to more than 20% . . . Salomon Inc., New York, issued an anti-takeover shareholder rights plan, which includes a dividend distribution of so-called share rights that allow a stockholder to purchase preferred stock . . . Coast Savings & Loan Assn., Los Angeles, completed the purchase of Data Line Service Co. from Costa Mesa-based Pacific Savings Bank on Feb. 5.