The 64 8.2 has smaller mounting ears on top of the housing. It will fit a 65, but to put a 65 rear (or newer) in a 64 the upper trailing arms need to be changed to the later years 65-66- +some 67 as the mentioned changes were in that year.The 65 -6-7 have a larger "hump" to clear the larger mounting bosses of the 65 up diff.
Trailing arms for the 68 and newer were a little longer, so it throws the pinion angle off.The differential mounts the same, so use the arms on the 65 that are there if you get a different rear, and it has arms on it, as delivered.
I realize the OP is working on a 65, just thought the info would be helpful to anyone else with a 64 in a similar situation. (like me) LOL
Remember too, after you install the rear, dont tighten the 8 bolts that mount the diff to the trailing arms and the frame.Tighten them AFTER the vehicle setting on the wheels and tires. Otherwise the mounting bushings start off being twisted too far and when you set the car down it will ruin them.Have the cars weight setting on the ground when you tighten all 8 bolts.Otherwise it will set crooked, moan, groan, pop and really suck.