Someone correct me if I'm wrong but I think the older tang style rugers were not CRF but merely had a large extractor.The new Rugers are true CRF mauser style actions.
This in a 458 could certainly work as a DG gun, but if you really want CRF for DG then you want a different rifle/action type.

If a big bore is wanted the 375 Ruger may be the best option for the conversion requirments with its standard length cartridge. No flies on that conversion.Should require alteration of other rifle components as well.