http://www.classicoldsmobile.com/tech/73.shtml
http://www.oldsmobility.com/10bolt-tech.htm
Measuring the ring gear will tell you which carier you have..that's what it will tell you.
A "real" 12 bolt as you called it, had an 8.875" ring gear.
http://www.drivetrain.com/gm8.875car.html