Unfortunately, I have this 'mystery' rear end in my 69 Cutlass. Here is what I know about it:
It IS a 12-bolt case with a 10-bolt carrier that measures 8.5", not 8.2". It was only in Cutlasses from 1968-1970. It is Oldsmobile's version of the Chevy 12-bolt rear end. It has an odd-ball bolt pattern on the cover, and the cover is almost completely round. The really strange part is that the pinion is only 12 splines, where as Chevy used a 28 spline for the 8.5".
It's main weakness is actually not the 10-bolt carrier. The weakness lies in the bearings. The bearings are smaller than the 12-bolt Chevy, leading to excessive heat and premature failure.
The main factor is the parts for the 'O' axle are 2.5-3 times the price of a standard 8.5" 10-bolt.
I am currently wrestling with the decision as to whether to retain the stock axle in a numbers-matching car, or to switch to a GM corporate 8.5" rear out of a 71-72 Cutlass. Either way, I'm upgrading the gearset to 3.42.
Hope this was helpful.