8 3/4 pinion angle

As I recall it is relative to the drive shaft, up or down.
(But that's on memory):-?
I swapped a 8 1/4 Diplomat into a Duster body. (It solved the puckered up rear end syndrome.) This is how I measured. That's what you asked.
Probably won't help you though since you are having someone else do it and not in the car.
I have the whole thing with pictures and explained if anyone want to try it.
I used the car for a fixture.
I checked the pinon angle of 71-4 once it was on stands. Put same angle on 8 1-4. That way it's apples to apples. (Springs are hanging down like this so it isn't a "real" number. In other words the weight of the car isn't on the tires.)

mesure pinion (Small).jpg

img291 you'll need to weld in fender washer cause the hole is bigger. (Small).jpg

img296 get it centered compare both sides of car (Small).jpg

img300 pull it back out and do a good weld. (Small).jpg