Not a big deal to turn to 30/06 into a .300 Win Mag. The bolt face and extractor need to be modified a little, but this is a pretty easy deal for an experienced riflesmith. There is also a little work to do with the follower and the feed rails of the action.

I would not do any of the WSM calibers. Not that it couldn't be done, but it is so involved that you would be better off just buying a factory WSM rifle.

If it were me, I would consider converting the 30/06 to a 30/06 Ackley Improved. You can make 3,000 fps with 180 grain bullets and a quality 24" barrel - with less recoil and better brass life than the .300 Win Mag. Just make sure you find a gunsmith who understands how the Ackley Improved's headspace. If your existing barrel is a 24" or longer tube and in good condition, you could just set it back and rechamber it to the 30/06 Ackley. Something to consider.