If the below linked site is correct, any '67 Ram-Air 400 cars had the 'UT' 3.23 , 'UX' 3.90 or 'YL' 4.33 rears only..
http://www.firebirdgallery.com/67codes.htm
So regardless of the 'N' casting, check your housing stamp and if a 3:55 stamped UW it's a cool rear but not from a '67 Ram Air car..
Weren't the GTO & Firebird 6-Speed showcars built five or so years ago called Ram Air 6 cars?.
~ Pete