Depends what Cortina !
I know that they can be adapted to fit Capri which comes with a bonus of p/steer on some racks.
Back to the shorter rod end thing...did you think of tapping more thread on the arm and then cut back to desired length . I'd get another rack and do this cause if it don't work. . It don't work !
Or cut the rods on a angle then cut ur 20mm at same angle , then shampfer the edges and Weld it hot to join it solid.. If this makes sense !