i had a Westley that had the scope which was put on the gun from the factory 1933 lettered out from Simon Clode stating that the engraver made a mistake while numbering the scope , gun number was 42331 scope was engraved 43221 it should say something about who does some ,but not all of there engraving

btw i apologize for overlooking the thumb cut,,,yes its most likely an FN...Paul