I respectfully disagree. The proof is my 69 A56 4 speed 'cuda 340 that has the original rear end and it's definitely a 489 case w/ factory 3.91 ratio. (built 6-13) This car has HD everything including front and rear torque boxes and a 15/16" diameter front sway bar. I think it was the combination of the gear ratio and 4 speed that triggered the extra HD stuff. Everything I ever read says the last model year for the 742 case was 1968. I don't have one in front of me but the 69 FSM probably does not have the 742 info in it.
All the 440 A-bodies were automatics. If Chrysler followed suit like on the Hemi and 440 B-bodies, it kinda makes sense. The standard rear in a Hemi or 440 car with an automatic trans was an 8-3/4. 4 speed Hemis and 440's automatically got the Dana.