Simplify3D gcode files begin with a series of comments that contain the settings used to generate that particular gcode file. If the gcode was sliced using multiple processes, ONLY the first (bottom) process's settings are listed. Additionally, only the active auto-configures' settings are listed. However, this may be a better starting point than starting from scratch on a custom profile.
To access these settings, you can go to File > Import FFF Profile within Simplify3D and select the gcode file. This will create a new profile with the settings from the gcode file, with the limitations mentioned above.