Try phoning John Knibbs, that's all I can suggest, as far as how or why the email didn't work I don't know, perhaps they don't allow attachments? I have no idea how their email system works. The BSAOG is independant of both BSA and John Knibbs International so we have no say or influence with or from either of them.
There may well be somebody on here who does know what you want to know but unless they own up I'm afraid I have no clue who that may be. Then again we may have no members with any knowledge of the gun you own.
I don't know but surely there must be a forum for classic or vintage English shotguns that may well have some members with the knowledge to help?