How hard/expensive is it to switch out gearing on an A-body?

oh boy...i have changed 3 on my own newer vehicles.
Go to any dealer and check his scrap bin and you will find many replaced weekly.
Yeah but how many millions did not fail. Ever?

You can find worn out tapered wheel/axle bearings in the "dealer scap bin" too! As well as any other part you can think of!

You are basically saying that the "Green" type axle bearings are junk. I'm saying that they have been used for 50 years in millions of vehicles. Billions of miles of driving. They are not failing all over the place!