The 31 spline axle is a worthwhile upgrade if you are really going to drive the car hard. I had mine upgraded to that with a built up Eaton posi in it. But as I said, I never had to do any narrowing or anything and I have talked to three others here who used the 8.8" and none of them had any problems. Must be the difference in the way the frame and rear end of the car is constructed.
Ron
