Good for you. I think a steel butt plate is fine. If you can find a good horn replacement, that works too.

The action shold be a good oNE for that chambering. As you say don't push it but they are stronger than some would have your believe. I like the 180 rn bullet in my 300 savage but a lot depends on the length of your magazine box and how it was chambered. Most factory 300 savages are short actions with space being at a premium. Short bullets rule. You may have more flexibility with the mauser. I use Reloader 15 powder.