For a basic standard-issue Clevo slushie, I doubt there is any difference besides the external casting. Could well be some different valve bodies in GT, ESP or Option 83 drivelines.
Some of the C4s for sixes had a weaker front servo system, but this was mainly limited to (US derived) imports.
You can get so much good gear for the C4, just build it into the right case; no need to root around adapting.
Adam.