Some interesting Holley history here but nothing specific on the introduction of double pumper carbs, besides the Dominator coming out in 1968 and to the public in 1970. But there are some suggestions that "double pumper" carbs were OEM on a few cars after coming out in the '60's..
http://www.rodauthority.com/tech-sto...or-milestones/
https://www.holley.com/about/holley/history/