AND NO DONT STAY AWAY FROM OLDS really the olds 442 rear ends are just as strong and yes they are different Internals and brake the pads are almost imposable to find as with a good gear ratio. But you can remove the Olds pads and inner guts and put in what ever you want. there interchangeable.
No, they aren't - and no, you can't.
Check this page:
Olds FAQ -- Differentials
Note this particular section:
The tern "n-bolt", as pertaining to the rear end of the car, refers to the number of bolts retaining the ring gear to the carrier inside the differential. Fortunately (or unfortunately), this number usually corresponds to the number of bolts holding the differential cover, so you can usually tell whether you have a "10-bolt" or "12-bolt" rear from the number of bolts on the outside of the casing. This is independent of the rear end gear ratio.
The Type O (Oldsmobile) 12-bolt rear ends use a smaller ring gear than the Type C (Chevy) 12-bolt, resulting in lower strength. The good news it that the Type O units retain the axle shafts at their outboard ends, while the Type C units use the infamous c-clips at the imboard end. This is why you see C-Clip Eliminator kits available for the Chevy axles. Also the Chevy rear has a "scalloped" cover where the Olds is smooth.
An Olds 12 bolt rear end is not a "true" 12-bolt. It may have 12 bolts on the outside cover, but it is a 10 bolt gear on the inside. The more common type "C" is very much different than the type "O".
A "true 12-bolt" has come to mean a Chevy c-clip 12-bolt rear. Oldsmobile 12 bolt rear ends differ from Chevys internally. In other words, the guts of a Chevy rear end will not fit in an Olds rear end housing, and vice versa. The phrase, "more like a 10-bolt", is usually talking about the size of the ring gear and/or strength of the carrier. The guts of a 10 bolt would not work or fit in a 12 bolt, and vice versa. There are differences between the 10 bolt and the 12 bolt both internally and externally.
Note also that there are two different ring gear carriers, one for 3-series ratio gears and one for 4-series gears. 3 series and 4 series carriers are for the 12 bolt Chevys. The difference is the dimension from the ring gear mounting flange to the pinion centerline, due to the larger diameter pinion required for the lower numerical gear ratios. A set of 4-series gears can be installed in the 3-series carrier with a spacer and longer bolts (not desireable due to reduced strength), but the reverse is not true.
The ring gear size is the size of the largest gear, parallel to the wheels. A 12 bolt Olds has a 10 bolt carrier that measures 8.3", whereas a 12 bolt Chevy has a 12 bolt carrier that measures 8.8". A 10 bolt Olds out of a 1971 has a 10 bolt that measures 8.5". 1968 and 1969 10 bolts might have an 8.2" ring gear. Starting in 1970, 10 bolts might be 8.5". Newer 10 bolts found under the last RWD Cutlass and Chevy are little 7.5".
Oldsmobile bolted the axles from the inside of the housing, whereas Chevy used c-clips. As for Buick and Pontiac, they used different types of posi actuating items called "cones" and "spools", whereas 12 bolt Chevys and Olds used what are called "clutch packs".
Type "O" Oldsmobile Rear Ends
The biggest weak spots in Olds rears are the wheel bearings and the availability of parts. Positive axle retention is good, but put in the new "updated" style wheel bearings for more strength.
Gears for the Olds 12 bolt rear are hard to find. The "O" was only manufactured for 2-3 years. So there isn't enough call for someone to start casting and machining new cases. While posi cases are not available (as far as I know) rebuild kits are. Unless the case you have is outright cracked or otherwise junk you should be able to rebuild it.