On Nov. 6, 1935, Sir Charles Kingsford-Smith took off from Lympne, Kent, in a Lockheed-Altair, Lady Southern Cross, to break the England-Australia record. He said it would be his last flight before settling down to aviation administration. Somewhere east of Allahabad, India, he disappeared. Eighteen months later, when he was almost forgotten, a wheel and a piece of undercarriage were found on the shore of tropical Aye Island, off the Burma coast. Photographs of the wheel were sent to Lockheed Aircraft Corp., makers of the plane. Last week Lockheed definitely identified the ship it came from as the Lady Southern Cross. Rangoon botanists, after examining weeds clinging to the wreckage, guessed that Sir Charles and his Lady Southern Cross lie in 15 fathoms of sea water close by Aye.