In the book The Concorder Story (5th edition) on pages 138 / 139 it talks about the crown modification with pictures of what was done. In
précis it states that the crown modification was to strengthen the top of the fuselage at rotate, it states that this was a candle sticked task which required the a/c to be jacked up so the skin has zero stress. The crown modification also included an additional strap over the fuselage just to the rear of the Center door. Appologies for the
précis of the text but I hope that this is of use. Oh yes the pictures of the modification are on page 140.