If you thrash your Mopar at road courses and autocross events (like Chris Birdsong does) with lots of hard cornering the Green bearings (ball bearings) can't hold up to the sustained high thrust loads. The vast majority of classic Mopar owners don't do that though so for most people they're fine.
Modern RWD cars equipped with IRS use unit-bearing hub assemblies which have a pair of opposed tapered roller bearings built into them to support thrust loads. Later-model Mustangs that still had solid rear axles used straight roller axle bearings that provided no side support but the axles were retained with C-clips inside the diff for thrust support. Same with any C-clip axles like the Chrysler 8 1/4", if you break an axle shaft the entire wheel/tire/brake/hub assembly slides out the tube and you're SOL but that's generally only an issue on bigger heavier vehicles with big tires doing offroad stuff, or a high-powered drag car that sees high torque loads from launching with sticky tires etc.
