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.)