I think I have mentioned this before - Qian Zhaohong, who is very highly skilled in XYlh, invested considerable time in learning (and has a great fondness for) Tongbei as well .
edededed:
The mechanics that I am referring to are shen/suo (stretching and contracting the spine and torso), rotation of the hips (both around the central axis and around a horizontal axis), spinal wave, extending from the bottom of the spine through the arms, connecting from the foot to the crown (and foot to the hand), opening and closing the joints of the shoulder and hips, extending from inside the joints etc. The three systems (XYLH, Xingyi and Tongbei) are the same in this respect - the mechanics are done the same way. The outward movements are somewhat different, but that does not change the foundation.
Re: Sha Guozheng - he is listed on Xiu Jianchi's student roster.