rear end question

It depended what was available that day when the car was built. Ive seen slant 6 cars with an 8 3/4 from the factory.

Not only that but remember back then when you ordered a car you checked off each individual option you wanted, unlike today when you have to take 20 other options to get what you want. That's why you see some cars with a /6 or 318 have a 8-3/4 rear.