Slant Six A/C throttle linkage or Cable...why?

I dont have exact answer. One would probably have to install the factory air components to discover the conflict with throttle.
That type of all rigid mechanical throttle linkage is/was fine for a push/pull lever in industrial application ( where it came from ) but it never was safe in a vehicle. In early automatic trans builds the throttle pressure linkage didn't have the slot for free throttle return either. Collisions or just a broken motor support would adversely effect these linkages.
There's a lot of stuff they wouldn't spend the money to re-engineer before designing a whole new generation. Then they went hog wild and engineered knee protection ( lower dash pads ready for 68 model production ). And that was immediately followed by the DOT lap belt mandate. DOH!
Anyway...
I would replace all that with 67 and later, firewall mounted pedal and all, a/c or not.