From my exp when I installed a NRG hub the only difference was there were 2 pins on the hub that needed to be removed for it to work. Other than that it slipped on both a 90 s13 hatch and a 96 s14. Never used any of those ebay ones since this I like to avoid issues like your having.
I'm not running a NRG anymore since I have moved on to a Works Bell Splash hub that has the SRS bypass plug.
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