Can I do this to a Krico 640s??
What would be required?

Anyone????

While I don't know what a Krico 640 is my answer would be the same for any repeater.

If your 308's barrel is not defective then it has value installed as it is. Even if it's bad the cost and potential problems to make the much larger WSM case feed and the added cost of the bolt face work make it a poor investment.

We can buy new M 70's here with a scope and mount in 270 WSM for $390. That's the way to go. Buy a new WSM rifle and keep, trade or sell the 308.