The big thing in a 9" is the bearing at the nose
of the pinion gear.. it controls the pinion deflection
and the 8 3/4 doesnt have it.. the pinion tends to deflect
and breaks the teeth off... on the back brace.. both are
sheet metal housings and will bend.. the back brace is
needed on both.. on a leaf spring car it bends front the
spring pads outward so you need the brace going to the ends