But downshift at the right place and the car turns beautifully. It's the engine braking. When I lift the clutch pedal after downsifting, there is definitely more braking force. Sometimes the read wheels even slip. So when I lift the brake pedal and turn in, the car is still braking into the turn, and doing it with the correct rear axle, without putting extra force on the front wheels that do the turning. And the car turns!
I guess a lot of my issues with driving the Mustang come from teh rear drum brakes. These are just too weak to match up with the fronts, and keep the car stable. But the engine braking helps in the rear and makes thecar turn. This is probably a good universal recipe for any RWD car.