Then spring pressure to the full rear position that returns it to the mid position
My recollection is that the earlier (pre 70 something) trans had a "Throttle Position" valve and later ones had a "Kickdown" Valve, might be a difference there?
BUT the return in 67 is a spring on the throttle lever itself to the Kickdown / Throttle position rod at the carb
the spring attaches to the post on the throttle lever. This is the 4BBL version, 2bbl is similar, and pulls the kick down linkage tight to the throttle linkage which will return the kickdown linkage to full forward position due to the throttle return spring.