Localized heat can be used to minimize distortion very effectively with  little practice.

The basic premise is that the heat is applied to a localized area to develop thermal gradients between the spot heated and the surrounding areas.

The best results are achieved when the thermal gradients are maximized. You can apply wet rags to the areas adjacent to the location being heated to help minimize the heat transferred to areas not being heated. I usually clamp pieces of angle along the edges of the area being heated and place the wet rags on the opposite side of the angles so the flame does not come in contact with the flame (for obvious reasons).

The temperature increase will cause the metal to expand locally, but it is restrained by the adjacent base metal that is maintained at a lower temperature. When the thermal gradient is high enough, the heated metal will deform by plastic deformation.  Once the metal cools back to ambient temeratures, the residual stress will be in tension with a stress equal to the yield strength of the base metal.

The temperature rise needed to produce localized yielding is not as high as one would suspect. A delta T of less than 300 degrees is usually enough, but it is common to heat the area to about 600 to 800 degrees  without causing undue damage to the base metal.

Since the material you are working with is Q&T steel, you must keep the temprature below the tempering temperature used by the manufacturer. You can usually get that information from your supplier or by doing a search on the Internet. I suspect it will be around 1000 to 1100 degrees, but you need to find out. 

When you apply the heat, the member will distort toward the heat source, i.e., in the direction opposite the direction you want it to go. Have no fear, it will move in the correct direction as the member cools. Remember, the trick is to apply the heat and confine the temperature rise to a small area. Don't let the heat dissipate into the surrounding base metal. Use a large heat source to heat the area quickly. You do not usually want to use a soaking heat.

I favor heating and cooling small areas so I can better control the outcome. If you heat too large an area the movement may be more than you had hoped for or you might not achieve the delta T you are looking for.

AWS publishes a standard on flame and heat straightening that is a very good source of information on how to apply the technique.

Good luck - Al