I don't want to argue how someone should do the "definitive" Superman II cut, but the idea of combining Superman 3+4 has a big flaw, the big plotholes in part 4! Okay, with the deleted scenes you probably can repair the damage on Superman 4, but the state those scenes are in...
Okay, most of us probably can ignore the damage to the print (probably even repair some of the damages) but the SFX scenes are mostly incomplete. To finish those, we would require the seperate scenes, not the composited ones. I don't see a solution for that. After all, we would end with a broken Superman 3 fanedit.