In August 1972 Bruce Lee wrote in a letter to his wife Linda that he had been working on a film script entitled 'Southern Fist, Northern Leg' and said he was definitely somewhere in ninth heaven. In the Golden Harvest/Concord Productions documentary 'Bruce Lee: The Man & The Legend' that came out just after his death in 1973, Bruce talks in Cantonese about some of the storyline. The meaning of the film is about 'What is the Truth of Martial Arts?' This was a man's journey of self-discovery as in the similar vein as an earlier script that Bruce had devised, 'The Silent Flute.'
From the title, we can interpret that this was going to be a period Chinese film as Bruce goes on a hero's journey asking various martial arts teachers and masters questions about 'What is the Truth in Martial Arts?'. The hero continues his journey and finally meets the 'Southern Fist' character who is fighting a group of men inside a tea house.
As in 'The Silent Flute' Bruce plays a hero seeking after an external object i.e. a book which will reveal all the answers about the Truth in Martial Arts. After passing the various trials and pursuing all the masters and teachers of martial arts, Bruce realizes that the answer is found inside yourself and it has always been there. As Bruce use to say, the journey is the most important part and not the destination. There's no magic book of answers. Everything - all the answers he was seeking were all inside him from the very beginning!!
The story would allow for as much Kung Fu action and philosophical quota as the hero would be fed a steady diet of external masters, teachers and authorities - allowing for a wide scope of action.