Missing Episode: Much of the original footage for TGoD is still missing, and it will probably never be found.
However, a documentary called Bruce Lee: A Warrior's Journey made in the early 2000's managed to find and piece together as much of the footage as they could find (which includes all of the fight footage from the upper three levels of the pagoda) but also reveals for the first time the movie's original plot, based on Lee's outlines and sketches. Really, it's a better use of your time to just look up the documentary than sit through the Robert Clouse version.
What Could Have Been: Before Lee's death, this would have been a mix between an action movie and a martial arts educational movie. The action side, involved a character named Hai Tien (Played by Lee) Who has to save his sister by giving his captors access to a pagoda they believe houses treasure at the top. The educational side was to showcase the different single styles of Martial arts through each Pagoda Level and how Lee's own Concept of Jeet Kune Do irons out many flaws in said styles.
From the finalized movie proper, producers initially wanted noted Bruce Lee Clone "Bruce Li" (real name Ho Chung Tao) to portray Billy Lo in the new footage alongside Kim Tai Chung. Presumably sharing the screen depending on who looked most like Bruce at specific angles. However, Li was three years into his career as a "leading" man and fed up with playing in Brucealike roles (making an exception for numerous biopics where he's obvioulsly an actor playing Bruce and not trying to fool audiences) and turned down the opportunity.