I have built several for T bucket type cars. Using a stock Ford or Chevy axle for the base of a king pin angle welding jig.
Heavy wall, 5/16-3/8", 17/8-2" tubing and bent with a pipe bender. Used bar stock, cut to length and bored/reamed on my lathe to kingpin size. Set the mill up at king pin angle and angle cut tubing ends. Chamfer the edges and use stock axle to set up the weld angles of the bar stock to tube.
Deepest drop was six inch. That one had some minor steering arm issues.
Not something an average guy coud do I suppose. But with ambition, fabrication sense and some machine tools. Very do able.