If you stripped the small 8mm stud while removing the pulley it'* because you didn't seat the 5/8" shaft against the SC snout shaft. While removong a pulley there is no load on the small stud, it'* only there the locate the pieces, as the load is transferred from the puller shaft to the snout shaft.
You must screw the 5/8" shaft tightly against the snout and then hold it there firmly while backing out the puller nut to remove the pulley.
The small stud is loaded when installing the new hub or pulley. Since most people use a small amount of anti-seize on the snout shaft, and the shaft has usually cooled properly by now. If not, use some water on the shaft to cool it before instalation as this ensures the shaft has its' minimal diameter.
Somebodt must have some good pictures while doing the removal and instalation.