From a recent article I read it seems that the prevalent style being taught in the Sha Cheng Village where todays "Wah Lum" system emerged from was initially a strong base for the spreading of the Mok Ga style.
Not being a Wah Lum exponet, just doing some side research that interlaced I see that some of the Wah Lum sets have a strong connection to Southern Fist styles
http://www.youtube.com/watch?v=tQMoktxgmMQ
http://www.youtube.com/watch?NR=1&v=...k&feature=fvwp
http://www.youtube.com/watch?v=WB57gVbiWi0
http://old.dongguantoday.com/localsc.asp?id=157