Is the only reason you want stepper motors to position that head at 4 different places? Because if so it can be done with 360degree servos and a decent transmitter that sends a 0%, 25%, 50% etc signal. Granted, not as accurate as a stepper, but from what it sounds like you're doing more than accurate enough. I'd expect repeatability below 5 degrees. Removes any need for Arduino, and makes the electronics very very simple.