I had the Ford 8.8 limited slip rear end and Superformance half shafts in my 2040. The left inner splines shattered within my differential. I prefered to not put the same parts back on the car, so I picked up a set of complete half shafts from The Drive Shaft Shop and replaced the limited slip with a Detroit Truetrack differential.
http://www.driveshaftshop.com/
The remnants of old Superformance spline material revealed little hallow spots and a metal of crystal looking structure within the center of the shaft. The outer surface seemed to be harder.