Take the drawing and the ball joint to Satellite Welding on Costa Rd in Concord. See Ben, he is the best machinist I have ever seen. It will cost about $100 for the pair. Oh, you do not need to make that large cut out section. It is there to install the cotter pin. If you find a ball joint with a Nyloc nut instead of a cotter pin you don't need to cut off that section.
He does need the ball joint in order to accurately measure the taper.