Can't help on the rebore part but I did have a 358 Norma Mag for a while. It's a powerful gun and you could do a lot worse in a bigger rifle than the big Norma. I used Big Game with the 200 gr TTSX for over 3000 fps and the same powder with the 250 gr Speer clocked 2750 fps easily. The barrel was 22" long and actually I still have it in the drawer, lol. A 300 Win Mag will need to be set back for a 358 Norma but you probably knew that already.
