DO NOT MODIFY THE SPINDLE
If you want to roll sender correct your control arm, you have 2 choices:
1- Instead of having a ballpoint at the end of the control arm bolting to the spindle, have a spherical bearing installed. Fabricate a long bolt that has the same taper as the OEM ball joint to fight snugly in the tapered orifice. Using a conical spacer and tubular "pipe shaped" spacers until the desired angle of the control arm is achieved. The bolt must be long enough to go completely through the spherical bearing, pass through another conical spacer, to allow full movement of the bearing, then cap it off with a castle nut and cotter pin.
2- Fabricate a offset bar to bridge the 2 tapered holes of the ball joint and tie rod. The bar has to be the correct height to correct the angle of the control arm since it is not adjustable. 2 tapered holes have to be drilled in the bar, relocating the tie rod and ball joint lower towards the ground than before. Generally this setup is used in drifting where they try to achieve more steering angle by relocating the tie rod pickup closer to the center of the spindle, thus giving you reduced steering feedback but increasing steering angle (changed the fulcrum of the tie rod assy).
Hope this helps, but don't modify the spindle, it's only a matter of time before it cracks, regardless of how good the welder is.
If you want picture examples of what I'm talking about, visit Driftworks website and lookup their Geomaster knuckle kits for Nissan 240sx/Silvia.