Stoeger kept the Zephyr name, but did indeed change makers from Belgian (probably Masquelier) to Spanish (Victor Sarasqueta)--most likely because there was a better market for lower priced guns.

The top end of the Stoeger Zephyr line of Sarasqueta-made guns (such as the Upland King) were true sidelocks. Pretty decent guns from all discussions I've read and examples I've seen, although they were neither Sarasqueta's nor Spain's "best".