A very nice find, Waidmannsheil! Scope and mount were certainly fitted post-WW2. May I draw your attention to a sentence in Rigby's catalog description of their "Take-Down" Mechanism: " We do not recommend this if our telescope sight is required." So you have to try out if the rifle holds zero after dis- and reassembling barrel and scope.
Well, I've got the same mount and a vintage Zeiss "Zielvier" scope on my 1905 made G.Gibbs Mannlicher-Schoenauer M1903 in .256 Rimless Gibbs aka 6.5x54 M-S. But the take-down feature was blocked solid when I had to rebarrel it. The original barrel was beyond any hope, bullets keyholing at 30 paces.