I have never done this before, but start off with the quad at ride height and measure the distance from the floor to the center of the a arm pivot bolts from the frame. Do this for both the lower and upper a arms. Also measure the off set the upper is to the lower (the upper a arm is going to be out from the frame a little more then the lower). Also check and measure the amount of rake if any the quad has (up swept angle of the a arms). Measure the positioning of the rod end at the bell crank in relation to the upper and lower a arms.
I would go with a 14" rack and pinion, now you can spread the a arms 14" and all the geometry SHOULD be the same as on the quad. If you use the bell crank the quad has for steering you will get bump steer.
