I straightened a mast that had bowed just above the spreaders using a hydraulic trolley jack and piece of heavy duty steam pipe. Strap the ends of the pipe/beam to the bare mast (about 18 inches away) using 3 inch lifting/tie down straps using several turns to spread the load area. Place the jack under the centre of the bend/bow which should also be in the centre of the beam. Using a wooden block on top of the jack to prevent point loading raise the jack slowly until a moderate reverse bend can be seen. Slowly release the pressure and check alignment. Repeat using increased pressure if required.
I have known two people to take the bend out a mast by sitting at the ends of the mast with the bend resting on a sand dune but the trolley jack method makes it easier to judge the reverse bend being applied to straighten the mast.
I reduced a bend of 5"-6" inches measured at mast tip to less than 1/8" on the unsupported(diamonds removed) mast.