Easiest to do, Gunwolf, is call H&H in London:
011-44 20 7499 4411
and ask for the gunroom. Whoever answers, just request the procedures to get a copy of the gunbook notes or a letter with details of original build and any subsequent modifications. You may luck out and the guy will wander over to the gunbooks and give you details such as the original caliber and whether Holland itself rebarreled the rifle.
Plan B is to go to the H&H website and noodle around until you find out how to request a letter.
Regards,
Tim
