Swamprat,
Gallyons in the UK have the Scott records and may be of help. If you can get a good digital picture of the proof marks, the historian at the Birmingham proof house can "read" them for you and can recount the history of the marks.
These things you can do yourself,but nothing is as good as the word of a competent gunsmith.
The cost of this gun is so high I hope you took the time to consider some of the London made guns. That price will buy you one hell of a Grant.