Its not that big of a deal if you are careful. The arm is forged steel and NOT cast. I did precisely what you spoke of; Turned the spline on a lathe to true it up. I used 5/8 steel flat stock and I carefully beveled the hole where I fit the Toy spline. I shaped it on a mill from wide to narrower at the ball stud end. I tig-ed it on both sides carefully letting it cool normally and then drilled a hole and pressed in a Ford ball stud. I will tig the rear of the stud so it doesn't slip. It won't anyway because I was precise as to the hole size. I used an expansion reamer to be sure. Mid-Fifties Ford makes (or sells) the pitman arm ready to go. I found it much easier to make my own and it is even stouter than any others I've seen.