Mopars of the era don't have axle windup issues like the Chevies do. In other words: The pinion snubber completed the system but wasn't really required unless racing supported the need for that approach. It was great for street cars of the day that saw some strip use.
The traction bar was added to try to resolve inherent deficiencies in the (Chevy) system. And like everything else, just because it fit their car, Mopar people felt the need to put them on their cars, too. They didn't accomplish anything, but added some little needed street cred.
