If the diff is not square to the car, the car will move to the side away from the direction the diff is pointing under accel., and to the other side under engine braking (not regular braking as much). Oval track racers use this to their advantage when setting up the car. A variable effect can be achieved by installing solid bushings on the left side and leaving the rubber on the other. This allows the rear end to point into the corner when on the gas, and to point out under braking to help pivot the car on turn-in. Doesn't matter if the diff is posi or not. The issue of excessive chassis flex still looms, but do some measuring first! I once had the pleasure (!) of driving a car (not mine) on the oval that switched back and forth between oversteer and understeer, depending on which bump it hit last. Later was discovered to have a broken frame (still finished third, though).
