Need one of these. I think a later 77 up b body wagon is same as well. I have the 12 bolt rear. Not sure it makes much difference.
Not trying to take away from a board member, but here is another option. https://p-s-t.com/i-23157776-1-rear...ake=BUICK||model=LESABRE LUXUS||submodel=BASE
Sadly my car did not come with one so I can't tell you what size the factory one would be. Though I would not be surprised if the factory one was the same size - 1".