All of the 8.5 car rear ends have 3 inch tubes, along with the 8.2 rear ends. The first gen Camaro and '68 up Nova rear ends are 60 inches wide overall and the 2nd gen Camaro rear ends are 61 inches wide. The 60 inch rear ends are going to be around 55 inches between the backing plates, which is not a good way to measure rear ends. You need to measure the total width.
The Dana 44 is a very good rear end. Maybe you should put new bearings in it and use it.