So what would be the correct setting to appear these front loaders ?
The correct setting is NOT have front loaders!! That's why we made it this way. Have you read the explanation ? I'll repeat it again:
Since these airplanes are too short, so when you call the catering vehicle, it will clash with the front loader, so we just removed in the default configuration that comes with GSX.
Of course, if you don't care if the catering will clash with the loader when you call it, you can configure it yourself, using the GSX airplane configuration editor.