I did the gsx.cfg's for all the 757 III models. I'll try to find it, and I'll see about uploading the file to the 757 III mods section to make it easier to find.

Edit. The link to the file is in this reply of mine in a big topic about GSX: https://www.captainsim.org/forum/csf.pl?num=1514864829/84#84