Unisys Corp. unveiled three Unisys A Series Smallframe computers, its first foray into the mid-size computer market where it will compete with IBM and Digital Equipment Corp. . . . Toyota Motor Corp., Japan's top auto maker, probably will form a sales and production venture with General Motors Corp. in Australia, Shoichiro Toyoda, Toyota's president, said president. But he added that the two companies were still reviewing the concept . . . Bicc PLC, a British cable maker, said it will buy an 80% stake in U.S. power cable manufacturer Cablec Corp. for $96 million . . . St. Louis-based McDonnell Douglas Corp. will build a 118,000-square-foot assembly plant for its Delta Rocket in Pueblo, Colo.