Thank you so much!
Honestly I just used observation of gameplay and screenshots, there weren't any other references I drew from. I identified the basic requirements of the system (position stored on 3 axes, snapping to available floor if Gomez is over a gap and there is any in front of or behind him that isn't blocked by a wall, keeping track of whether Gomez is hidden from the camera on the back layer or not, etc.) and came up with my own ways to implement them. I actually ended up having to use a separate collision function for each of the four perspectives. If you really tinker around with it you'll notice my approach isn't actually a perfect recreation of FEZ's rotation system, because Gomez always gets pulled to the front in mine instead of staying in a fixed place when rotating.
Also, the actual rotation effect is purely visual trickery - the model's layers (which are just collections of 2D sprites drawn with depth ordering) get a horizontal offset based on distance from the model center, the perspective switch is masked by the sweep effect, and then the layers settle back into place.