Finally got my Quick Performance 9" rear mounted up to my '72 Cutlass. What threw me for a loop is the pinion is offset to the passenger side by 1". I called up QP and they said "For 68 to 72 applications, we build the rear with the stock 1" offset."
I've had a couple of 8.5" bolt-in axle rears in my hands and both were centered. Is this offset a Chevy thing? My buddy has a '70 Chevelle with an 8.2" but I can't recall if it's offset.
Not a huge deal, but I'm running full size mufflers and a 3.5" driveshaft so it's pretty cozy in there.

Separately I was checking driveline angles, and with the chassis more-or-less level (not exactly a good flat surface to check), the trans yoke is at 4.5 degrees down towards the back of the car. I put 3/8" of spacers under the trans mount but that didn't change it much. First time I've bothered to check the trans angle. Is this typical?
I've got a 350 D block, using a stock big block mount on the passenger side and a driver's side poly mount made by .... shoot, can't find his info now. The engine sits higher than it used to with small block mounts (I know, I know, they're supposed to be externally identical, just saying what I've seen) - it's way harder to mess with #8 spark plug than it used to be.

 

I asked the driveshaft shop when I ordered the new shaft and they told me 1/2 to a max of 3 degrees on the angles, opposite and as close to the same as possible, with in 1 degree.
I have the same issue with aftermarket motor mounts on the 66 , they sit the motor alittle to high , had the same as you 4.5 degrees down angle , I used a trans mount I got off amazon and 1/8 shims and now it's at just under 3 down and the rear is 2.2 up. I hope the new aluminum drive shaft doesn't hit the tunnel as it's very close.
I don't remember the pinion being offset but I have a spare axle out of a 68 I can measure if you would like