['ol Pinion head]

Greg,
Hello, I've given a disclaimer on the Oldmobility site info, since I first saw it. While it is a graphically neat site, it lacks the quality info that someone like myself who's built the 8.5 for a long time has run across. Not going to get that info w/o pulling a ton of cores/ assembling rears.

One of the omissions... for years, website article exspurts, & most recently an article in Carcraft, have stated "look for the big squared off casting lugs to ID the 8.5". Since some 8.5 housings lack this feature, not the best info. Also in an order to disquise an 8.5 & make it look like an 8.2 from the rear, many builders have reshaped the lugs on 8.5 hsgs to make them look like other 10 bolts, I've done this for years on the most common 8.5 A-body housing.

Here's a list of common 8.5 ID points.
-All 8.5 rears have twin cast ribs on the each side of the cast hsg. Similiar to 12 bolt Chevy hsg. These add support to the pinion bearing area. This pinion area is slightly longer on an 8.5, couple that with slightly longer pinion flange, & that is reason for 7/8-1 1/8" shorter driveshaft needed when swapping to an 8.5.
All original 8.5 r/e's used stamped steel straps & bolts to attach the u-joint to the pinion flange. One 12 bolt flange also used bolts & straps, but most 12 bolts & all 8.2 10 bolts used pinion flanges that used u-bolts, & nuts for u-joint attachment.