I did some research on this 2-3 years ago, and discovered that the reason "assembly" was moved to Portugal was the assembly in South Carolina was at a plant mostly focused on military rifles. Consequently they did not know how to deal with walnut stocks--and the Portugal gunsmiths did. Which is why the assembled-in-Portugal walnut stocks are pretty nice--and the rifles shoot so well.
I know the last from buying and shooting some of the Portugal-assembled rifles, rather than guessing. They are more accurate and reliable out of the box than pre-'64 Model 70s--and the most recent New Haven rifles.
