You can check
www.JDRace.com in the rear ID section. The 1971 8.5 has 2 straps and 4 bolts that hold the u-joint in place. The 10 bolt 8.2 has 2 u-bolts and 4 nuts that retain the ujoint in place. That should help
And of course this must have 10 bolts on the cover.
If you have a true olds 8.5 the rear cover will be round and have a passenger side bend /ripple in the upper 2 oclock position . (reference picture)
Some Buick 8.5 were put under the olds rears also which have covers that look almost like the 8.2 covers BUT they do not interchange because the 10 bolt pattern for the cover is slightly different. this cover has 3 and 9 oclock scallops in the cover like most 8.2 rears.
Hope that helps