I don't think the bottom rifle is a .450 to start with. Note the short action compared to the .303.
The gun pictures might be reversed though. I see no bolt, but a curios flat piece of steel emanating from there the bolt should start.
Also, I would suggest the picture reversal is correct, due to the "weight" of the top rifle's stock and lack of pistol grip & slimness of the grip on the lower one.
Also, the lower rifle has a ladder sight which might better fit a .303 than a standing blade and leaf-sight system the upper rifle has.