6405 & 6406 numbered carburetors are listed in the Holley Illustrated Parts & Specs Manuel, as 1972 Chrysler 440 Eng. Spec. 3 X 2 BBL. Front Std. & Auto. Trans. Calif.
So those numbers did have an application from the get go, in the beginning.

RF-4C Phantom 69-370 Zweibrucken, Germany