That is an interesting article. It reinforces my past comments and observations.

35 spline S-60 rearend assemby 191 lbs.

31 spline 9" rearend assembly 174 lbs.

If you compare apples to apples by adding 35 spline axles, and a backbrace to the 9" housing and fill both rearends with gear lube you will find virtually NO weight difference between the 2. When you add a Fab housing, the 9" assembly weighs MORE.

Ford engineers increased the oil capacity to 1 GALLON in the early '70s to combat premature wear due to the heat and friction generated from the inefficient 9" gear design. In contrast, the larger 9.75" Dana 60 rear takes about 2.75 quarts.

The heat/friction issue is well known among circle track guys because it becomes an increasing problem the longer those rearends are run. When I used to build circle track rears, I had to set the backlash wide and the bearing preload loose to keep them from burning up in competition.