It's G&H #2546 (Winchester action #556837) chambered for .264 Winchester Magnum cartridge. Must have been made shortly after this cartridge made it's bebut. That was RMs pride and joy (his initials appear in stock oval), since he sure took care of this rifle. RM sure knew how to order a fine rifle.
As stated it handles beautifully just like a fine shotgun not something I expected after seeing weight figures for used sporters at Griffin & Howe site.