Whoa Hold On A second are you saying you were able to hack it so Culling is forced therefore we cold revert back to the original DFF Files? I mean History of The 2DFX problems go way Back:
VC: DFF Files created had all sides including Reverse Faces.
GTA3: DFF Files only had needed sides Reverse Faces were Drawn Via Culling:
GTA LC First Solution: Killer.ip and Myself single handedly added all faces to the dff files that needed the reverse faces drawn however in doing so the dff files grew in size. and No light DATA was saved making the effected dff files blend out from other dff files.
GTA LC Second Solution: Addinf "x"_rev.dff files to the gta3.img these files were only the missing sides needed and were added to the map aswell. DFF Files and IMG Grew and 1 side of the effected buildings had no light data.
GTA LC Third Solution:
Using Blender added all faces to the effected Dff files preserving the light data. DFF Files grew in size.
If what I think you were able todo is true it would be the best implemented solution as it will gaurentee that we wouldn't have missed any dff files that did not have the reverse face drawn and will bring down the img file size again.
Forgive me if I have missed alot as I have been away from GTALC for a long while.