Oh sorry, it does actually have them, but look at the time stamp, IllusionInjector.dll & IllusionPlugin.dll in StudioNEO_64_Data\Managed in your GGmod for NEO.7z are 2016-06-17 while those in IPA 3.3 are 2017-04-xx.
Hmm, are you sure they came from https://github.com/Eusth/IPA/releases/download/3.3/IPA_3.3.zip ? The newer IPA doesn't have IllusionInjector.dll & IllusionPlugin.dll.
Thanks for the MOD, does it support the new version of the IPA here? https://github.com/Eusth/IPA/releases
It seems the most newer plugins including the wide slider are moving there for the party support.