I'll do my best to answer your question.
HungFutKune,
I first would like to start off by saying that the Moi Fa Kuen is not a part of Tang Fong's lineage. He Sigung is Ho Lap Tin. Ho Lap Tin trained with Tang Fong since the time he was in China teaching at the Yi Yong Tong. Ho Lap Tin learned everything that Tang Fong taught and taught these things to his students as well but the Moi Fa Kune set was not a part of the curriculum.
The Kuen Toh (Fist Sets) which were taught by Tang Fong are;
1.) Gung Ji Fook Fu Kuen
2.) Fu Hok Sueng Ying Kuen
3.) Ng Ying Kuen
4.) Gau Duk Lin Waan Kuen
5.) Teet Sin Kuen
Although there are some physical differences between Lam Sai Wing's and Tang Fong's system of training, the faht (method) is still the same. More or less the shape of some movements are different, but the applications are the same.
The other difference is that Tang Fong lineage breaks the Gung Ji Fook Fu Kuen into two different sets because of the lenght of the form which is hard for some beginning students. The form is broken into Gung Ji Kuen and Fook Fu Kuen. Also, Lam Sai Wing's branch does not teach the Gau Duk Lin Waan Kuen.
I hope I was able to answer somethings for you.
Peace
Jerry Battle
The Southern Fist Subdues The Fierce Mountain Tiger