What you do is find an old king pin. (Other half inch bar is available). Grind a taper about half the length that reduces the diameter down to 3/8 or so over half the length. If inserted from the inner side it will help align the axle with the spring bush. Then insert the pin and push it in, maybe with a hammer and brass drift until the pin is about 1/8 away from the spring bush. Take a deep breath and whack the spring pin with the hammer and drift. It will push the king pin out and the spring pin will be in position. Simples.
Alan Fairless