I'm assuming you don't own any No. 1s.

The ejector has to move sideways as it is not like an original High Wall (for example) where the extractor (no ejector) only moves out enough to get the rim clear of the chamber where it can be dumped out ot pulled out with a fingernail. In the Ruger the ejector is spring loaded to snap the cartridge out of the chamber and the rifle.
The ejector when open sits way back in the action and to the left of the chamber axis. The next shell loaded (rimmed or rimless) drops into the chamber going right past the ejector. The the breech is closed, a roller on the breechblock side pushes the ejector forward until it contacts the rim. It then moves left (like a modern Mauser bolt action moves right and snaps over the rim) until it clears the rim at which point a spring and plunger push it to the right behind the rim. To work correctly there are two critical factors:

-the ejector must have a contour on its front of the hook that will slip around the rim.
-the ejector arm must be pushed far enough forward to get behind the rim.

Problem 1: Since the 450 #2 rim is .650 the 458 WRA only .532, getting that lateral move to the left is difficult

Problem 2: The 458 ejector (modified) that came in my rifle has an arm front to rear dimension that is abou 5 thou less than the new 416 Rigby, that may just enough to prevent by just a skosh, the ejector from sliding behind the rim. (As by just dry firing it, the 458 one is jarred enough to snap behind the rim)

Tomorrow I get out the stones and start (hopefully finish) getting the right bevel on the front of the 416 hook to allow it to slide around that huge rim. The transverse spring may need to be lightened to lower the resistance of moving the ejector around the giant rim.

More to follow. Thanks.