Hello, the story you recount sounds exactly like what is presented in the documentary "Bruce Lee: the man and the Legend" (as well as another docu, "Bruce Lee, the Legend") which has a few minutes of Shiu Hon Sang talking about Bruce, trading lessons for Cha Cha. Shiu Hon Sang to my knowledge was not a Tai Ji Sifu, but a graduate of Jing Mo (Chin Woo, Jing Wu, etc) and therefore taught many Northern style forms.