There are a couple of ways to accomplish what you want.

You could use a CRF WSM bolt head, and your front baffle you have now. Your action has not been cut for the standing ejector (like many of the staggered feed RUM's, WSM's, and RSAUM's are).

You could take a long action magnum bolt head, trim the tail end .190", and use the front baffle and firing pin that you have.

Or you could buy the new short action heavy magnum (9/16" lugs) bolt head, and relieved front baffle. Going this route, you will need to purchase the longer firing pin.

There are WSM staggered feed magazine boxes, but I don't think you need one. Just tweak the .308 box you have if you run into problems.

Think I'm right with the advice I've given, if wrong hopefully someone corrects me.