Im not familiar with the speedway brackets. Are they bolt on or weld on? I had a guy bring a car to me with the same symptoms. He bought and installed weld on brackets on the rear axle. They were not square to the rotors. All I did was cut them off, had the boy apply the brakes, and welded them on correctly. No bleeding, great pedal.
Before doing any of this, I had the wheels off with the rotors bolted in place. Watched each wheel as he applied the brakes. You could see the calipers on both rears move at angles.