The end of the axle already had a center hole, I suppose from when it was made. The drill bit just curled up on its edges. Never even made it to the bottom of the centering hole. I was only trying to drill it because it was already chucked in the lathe.
Got to go buy some tube for the boom. I think I am going to try and find some weld in sprocket hubs or taperlock bushings the right size to fit the axle. The sprocket hubs will already have a keyway cut in them so all I have to do is grind a slot in the shaft. I had a 1 7/16 taper lock bushing, but it was to big. Dont know if I can find one to fit local, but if I can, I think using a taperlock and grinding a keyway and welding my pitman arm to the sprocket the taperlock fits into, should work. Tightening the taper lock should keep the pitman arm from falling off.
I have came up with all kinds of ideals that should work since I started this thread. Not sure of which ideal is the best, but all should work. Not sure about the pressing teeth in a collar as I first considered, but I am sure some of my other ideals will be a lot easier.