Arrow Electronics has amended its previously announced agreement to purchase Cypress-based Ducommun's electronics distribution business. The changes include elimination of a clause conditioning the deal on the closing price of Arrow's stock. Arrow, a Melville, N.Y.-based electronics distribution company, is purchasing Ducommun's Kierulff, Ducommun Data Systems and MTI Systems businesses, which accounted for about 80% of Ducommun's 1986 sales of $455 million. Arrow's stock has fallen sharply since the Oct. 19 stock market crash, recently trading at about $6 per share, compared to between $9 and $10 when the Ducommun deal was announced in September. The original purchase agreement included the condition that Ducommun could cancel the deal if Arrow's stock price fell below $6 per share for a period of 20 days before closing. Arrow officials said the purchase price remains between $125 million and $135 million, payable in stock and cash.