SPARTECH<SPTN> SETS REVERSE SPLIT,DEBENTURE SALE Spartech Corp said it plans a one for five reverse stock split and has filed a registration statement with the Securities and Exchange Commission covering a planned 25 mln dlr offering of convertible subordinated debentures due 1999. Spartech said the debenture offering will be underwritten by Kidder Peabody and Co. The company said the split will be effective on stock of record April eight.