Taft Broadcasting said its directors approved participation in a joint venture with Texas financier Robert Bass to acquire Wometco Cable for $625 million, but Taft added that the percentages of ownership and financing have not been determined . . . Centrust Savings Bank of Miami said it has reached an agreement to buy all of the stock of Old American Insurance Co. of Kansas City, Mo., for $115 million . . . The just-harvested California almond crop is down by almost half because of brutal storms during the bloom last February. The walnut crop also is reported to be about 13% below 1985 because of a steady rain that kept bees from pollinating.