MARK IV <IV> STARTS BID FOR CONRAC <CAX> Mark IV Industries Inc said it has started the 25 dlr per share tender offer for all shares of Conrac Corp that it announced yesterday afternoon. In a newspaper advertisement, the company said the offer and withdrawal rights expire April 20 unless extended. The offer is not conditioned on receipt of any minimum number of shares but is conditioned on the arrangement of financing. Mark IV already owns about 9.9 pct of Conrac's 6.8 mln shares outstanding.