The game does not allow gamepad and mouse input (emulated by vorpX for head tracking) at the same time, hence I had to enable vorpX’s built in gamepad to mouse/kb mapper. Otherwise gamepads wouldn’t be usable at all together with head tracking.
I set up the key bindings to mimic the game’s native gamepad mapping, but you can change the button mappings to anything you like in the vorpX menu on the input page.
BTW: You might find using your VR controllers instead more convenient. They are also freely configurable in mouse/kb mode. For VR controllers vorpX displays the current mapping on the ingame controllers, so that’s more convenient to use than having to remember the gamepad mappings.