Stu Brennan also attended the 1972 New York Auto Show and he took pictures of two of the 2.5 challenge participating cars that appeared at the event. The current New York Auto Show is held in April so if it was the same back then this would have been before the start of the 1972 season. See these pics and others taken at the event here:
http://www.pbase.com/sb_photos/ny72