A 180 turn can definitely be performed within 600 feet, but then it has to be done quickly, with a good bank angle, and there is little room for adjustments in elevation. A safe 180 turn type of approach (naval aviator) requires (I think) bank angles that are less than 45 to have the room and time to adjust the rate of descent. In some way it is like having a curved base leg. But you may not do it safely if you are too close.
Please Dan correct me on this, I am not used to do the naval pattern.