Been awhile since I did any Chevy clutches, but if I remember right there was a long and a short throwout bearing available to make up for the differences in the input shaft collars..... Hopefull one of the chevy guys will jump in. I've switched to the hydraulic throwout bearing and master cylinder on everything. The initial adjustment on them takes a bit longer, but they sure do hold up better then the mechanical linkage powered throwout bearings.