Stock 8.2, type "O" 67-70 Olds, or 12 bolt driveshaft will need to be shortened 7/8-1 1/8". The "nose" on the 8.5 housing, along with the pinion yoke are both longer & require the shorter shaft.
64 model A-bodys used their own specific upper rear control arms & swapping in anything other than original '64 rearend will require use of '65-67 upper control arms.
64 through 66 A-bodys used a different rear spring, than '67 & later. The 64-66's had a bolt-on "ear" that clamped the rear spring down. One can trim the spring guides of the later rear & weld small square plate on then use the clamp on ears, OR one can go with later model springs.
Width issues... Width changed DURING the 66 model year on BOP 8.2 rearends. Have ran across this in parting many 66 Tempests & LeMans & have been trying to track down exactly when this happened out of all the BOP A-body plants...for many years. Ck'ed our records & in so far custom building & selling now 317 early 8.5 A-body r/e's, the main tight fit issues I've run into were when installing 8.5 A-body rears under a pair of 64 Chevelles & a 65 Elco. The wheelhouses under the '64's & 65's are the smallest of all A-bodys & customers in two cases were running 275-60R15's on aftermarket 8.5" (9.5" overall) wide wheels. Correct offset wheels were a must for such tall wide tires & even then, the tire-wheel combo is getting cose to the 1/4 panel lip. Never have run across this problem on a 66 or later, but on one of the 64's, we had to actually jack the Chevelle up with the shocks unhooked, bolt the wheel & tires on, then carefully let the body & chassis down & then reattach the shock mounts. Would not have had to go to this trouble with a 255-60R15 & a different wheel