Thanks
@rookhawk for your thoughtful and comprehensive reply.
The mount I am chasing does not have a rear double claw, although I have seen that style on other rifles.
The mount is by H&H for an H&H magazine rifle. Photos attached show;
1. the locking lever on the rifle,
2. the mount itself, which is a single fore and aft locking lug integrated into scope rings, which are joined by a rod, and
3. the scope mounted to rifle, for context.
Your price estimate from previous discussions with Rigby will be a useful guide. We are in Oz, so between restrictive firearms laws and Wuhan Flu logistics bureacracy, getting the rifle to H&H in UK may be a palaver. I do not know that H&H have an Australian rep, unlike your siutation in the US.
Alternative I may have to either delay the project until we can travel again, or find a reputable local engineering firm.
I shall see what can be done.
Thanks again.