http://www.defencetalk.com/pictures/data/3238/F-7_SABRE-II.jpg
I think everyone can differentiate which one is F-7 & which one is Sabre-II. The Sabre-II initiated for the modification & modernization of PLAAF's F-7s.
Sabre-II project was initiated by the Chinese in cooperation with Northrop Grumman. Due to political uprising in China & its suppression by the Chinese authorities United States pulled Northrop Grumman from the project. The project however was restarted under the name of J-9 later turned to Super-7 under CAC. CAC invited Pakistan (PAF/PAC) to joint venture & Super-7 was renamed to JF-17 & FC-1 with the aircraft completely & radically modified.