It will be a Greener 'Rational' stock at a guess. Some design that Greener played around with. You will find reference to it in most of Greener's books. I've heard the fences refered to as Dougall fences and I have something very similar in style on an old Tolley boxlock. Most unusual on a Greener. As Roy says, I'm sure Grahame Greener would be most interested. Lagopus.....