The only one I know of with a 31mm stack height is the DuraAce HP-7600...make sure of your measurements, don't just measure twice, make it 3 or 4 times and use a digital caliper and follow good instructions (like Sheldon or Sutherlands) so you know you're right. If you are then that's a very short stack and probably NOT done with the original fork at factory for the stock HS. AFAIK all the Stronglight HS were from 34.0 (P3) to 40.7 (Delta). Campys are all going to be in the 39 to 40 range except for a Pista which still is over 31.