[Jim Kaekel]

You may be referring to an "O" type rear that was made from '68-'70, commonly found in 4-4-2's, Cutlass, etc. in those years. It has a smooth, 12-bolt cover and a 10-bolt carrier. There are no spools, aftermarket axles, etc. available for it, so it would not be a good choice for a race car. If it is a limited slip style and has 3.42 or 3.91 gears, it would be fairly valuable to an Olds enthusiast and you could easily get good money for it and then buy what you need, a 12-bolt Chevy.