8 3/4 inch rear end lie angle

Perch relationship to the pinion and pinion angle in the car are two different things.

Here's one post from Cass, AKA Dr. Diff. Says the same pinion to perch angle, pinion slopes UP 5* for stock setting on an A body 8.75 rear.
http://board.moparts.org/ubbthreads/showflat.php?Number=5805168

If you are going to set up the pinion angle in relation to the trans, set perches in the car.