How precise? If you use matched motors and reduction gearing so they are not heavily loaded you will get reasonalbe control just with PWM. For more precise you need shaft-encoders and then close the loop to make two continuous rotation servo motors.
If the winch drum is not precise then your position feedback can't come from rotation, you will need linear position sensing of some form.
If all you need is to keep a platform level while winching both ends you just need an accelerometer to measure tilt of platform? Or use one motor
Stepper motors will be very slow and inefficient BTW and thermal issues may need addressing.