My friend has a '71 Cutlass that appears to have the original drivetrain. The rear diff cover looks like the BOP 10-bolt with the scallops in the sides, but the rear also has the "ears" on the bottom of the housing that are typical of a 8.5 "corporate" 10-bolt.

Is this a "good" 8.5" rear, BOP rear, or some weird configuration? What would a 350-4bbl, TH350 equipped '71 Cutlass have used for a stock axle?

It is the 8.5 corporate rear end. It takes all of the same gears and differential parts as any other 8.5, but it doesn't have c clip axles in it. This is probably the best 8.5 because of that. These were only made for a year or two, so they are pretty rare. If it had the round cover then it would have c clip axles.

Freddie ,are you sure about that ?
Think that one does have the c-clips.
Didn't know of an O type 8.5 corporate rear ,only the ones with the 12 bolt covers.

The first 10 bolt 8.5 rear ends that were used in the A body had the 10 bolt cover with the sides cut out. These had bolt in axles. I've had some and built some for other people. They use all of the regular 8.5 parts except the axles and axle bearings. This is not the "O" axle that was used in the Olds from '68 to '70 with the 12 bolt cover.

The first 10 bolt 8.5 rear ends that were used in the A body had the 10 bolt cover with the sides cut out. These had bolt in axles. I've had some and built some for other people. They use all of the regular 8.5 parts except the axles and axle bearings. This is not the "O" axle that was used in the Olds from '68 to '70 with the 12 bolt cover.

That's good to know. I did not know if Posi units were the same or not. I assume these are 28-spline axles?

My friend is planning a 455 swap eventually, and he was wondering if the rear would be strong enough. I would think that a corporate 8.5 w/ bolt in axles should be plenty strong for a 455 on street tires, and there are a lot of posi units, gears, etc to chose from if everything is the same as an 8.5 corporate axle.

This does have 10 bolts in the cover, right? If so then the Eaton for the 8.5 will work. Yes is has 28 spline axles. The Eaton Posi is $435 plus shipping. You will also need bearings and shims to install it. They run about $45.

This does have 10 bolts in the cover, right? If so then the Eaton for the 8.5 will work. Yes is has 28 spline axles. The Eaton Posi is $435 plus shipping. You will also need bearings and shims to install it. They run about $45.

Yes. It has the 10-bolt cover with the cut-outs on the side like this:

http://www.oldsmobility.com/images/10boltGM-Pcover.jpg

But it also has the "ears" on the bottom like the arrows show:

http://www.oldsmobility.com/images/chevy85-10bolt.jpg

That's what I thought. It's the 8.5 10 bolt.

That's what I thought. It's the 8.5 10 bolt.

Thanks... I'll pass along the info. :)