There were two different Chevy rear ends in 68--the 10 bolt and 12 bolt. The 12 bolt came in the 396 cars and in the station wagons, the 10 bolt was in most everything else. Count the number of bolts holding the cover on. If it is the 12 bolt chevy, it is better than the GS rear end, if it is a 10 bolt, it is not as good as the GS rear end (GS rear end had specially hardened gears and larger axle bearings).