If you can find a 35Whelen as a donor action for the 358Norma that would be good. All you would need would be to rechamber it. I prefer rifles with long magazines so I can long throat the chamber and seat the bullets well out. Better velocity with no, for the layman, noticeable increase in pressure/recoil. But where this stands out is with the heavier/longer bullets.

I have done some, but not much load development with the 358RUM with the 275 and 310 grain Woodleigh bullets. I'll track down the data I have later in the day and let you know what I have achieved so far. They are a viable option in the 35Whelen and 350Rigby Magnum, which can safely be loaded to match the 358Norma.