Looking at the various different forum responses to posts about the .458 MS, all of the photos I see and some of the info on the Mannlicher Schoenauer Collectors page says that the .458 MS were all made with swept back bolt handle and the Monte Carlo stock. Mine has a straight bolt handle and a normal, (thank god), stock. I wonder if it was a custom ordered rifle.

https://www.youtube.com/watch?v=PxIaoMFeO1E