Jim G;
That "different drag link and pitman arm" actually goes back to and includes the '53 models. That spline pattern you describe sounds exactly like the stock pattern for the '53.
Your new box was made for a particular application. Why make a new pitman arm, why not just use the stock arm for that application and modify it if need be. Did you test fit your stock arm? Chances are it fits.
I dunno, is that an oversimplification? I just don't see a need to reinvent the wheel here.
