The hypoid offset of a Dana 60 is 1.125" from the carrier centerline. This means most of the force transferred from the pinion to it's ring gear is mostly up/down, not so much trying to force the carrier out the back. Caps don't have to be that strong.

The book I have doesn't say what the offset is on a 8.75.

The Ford 9" has 2.38" of hypoid offset. That much offset makes the pinion teeth look more like a worm gear, pushing at a much lower point on the ring gear. This translates to more force trying to push the carrier out the back.

Grant