I'll offer a thought on the barrels...
I wouldn't re-chamber the 308 Win barrel. Just pack it up in a mailing tube, along with the std bolt head, and tuck it away someplace for the day you might want to switch back. Yeah, 308 Win isn't sexy, but it is a pretty useful and easy to obtain cartridge.
For the new barrel, I would get a stainless steel pre-fit from a reputable maker. Pac-Nor is my favorite barrel maker, but there are others than make good product too. That way you can make choices on the twist rate and length based on what kind of shooting you want to do with the 300 WSM. If you have reliable access to a lathe, then you can keep backing the barrel up and re-chambering it over and over until you run out of barrel shank to work with.
That's just my take on it. I've re-barreled lots of rifles over the years and tend to spend the extra money on a good initial barrel. Knowing that when throat erosion starts to harm the accuracy, I'll take it down to the lathe in the basement and re-chamber it. Making it ready for another few thousand rounds.
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