If it is a true Olds 12-bolt, it will bolt into your Chevelle fine except for the U-joint as Havoc mentioned. You can also get around this problem with the use of a conversion U-joint; it is expensive but fairly commonly available. HOWEVER, this is a completely different differential design. The gears, carrier, axles, yoke, everything is different than the Chevy rear ends and are not interchangable.