In late 70 's was over long beach area at 3,000 ft in a C 340 getting set up to land at LAX when I found myself nose to nose with another aircraft opposite direction about 3 seconds away. I rolled inverted and pulled back just enough to give us about 50 ft clearance. About a second before he passed he made a right climbing turn so kept my wings parallel to his then rolled back level after passing. I didn't file a report.