When we started relaying the Welsh Highland we sprung the rails into place using crowbars but quickly found that there was a tendency to develop angles at rail joints, no matter how could and strong the fishplates connecting one rail to the next.
We also used a rail bending machine whose name I cannot use on an American website but which used a powerful screw in a very heavy cast steel frame to bend the rail.
The real thing though, which we have only discovered the last two or three years, is to stagger the rail joints through the sharp curves, so each joint is supported by whole rail on the opposite side, rather than the joints in both rails being opposite each other.
Bob Gartside