Installing new rear axles

Im having difficulty installing some new rear axle shafts made by us alloy into a 2001 camaro that is equipped with the 7.625 ring gear and a torsen carrier series 2. When I install the c-clips and seat them the thrust block wont fit in between the axle shafts. WHAT changed to make it not fit? The new axles are supposed to be an oem fit.