If I were doing it, I'd simply run the 308 win brass through the 7mm-08 sizing die and then check to make sure the mouth of the case was the size I was looking for to seat the bullet. Sometimes when you size down like that, you need ream the case mouth to be able to fit the bullet without crushing it or sizing it down. Otherwise load as you would normally, backing off 10% and working your way up if things look ok. You may have to trim the case too.