Mine made it into the 10.20 range, but was 60'ing around 1.30 range. Car weighed 3200#. Then is started clearing ring gears on a regular basis. Went to a Dana 60 then. As for a 68 Dana in an F-body. The spring perches will be inward 1/2" on each side. You can put one side on the pin & bolt it in place. Then just use a strap to pull the other side in. Only 1" total difference. The spring will go in that amount no problem. Have put 2 68 8 3/4's in my F-bodies w/no problem's at all there. Lots of tire space w/right offset wheels
Thanks, Ken