Although I had brass fitting on my 67 Econo's king pins they still wore out and needed a machine shop to bore and campher (if that's the right word). I'd try the Delrin fitting because it is a very tough form of nylon. However, since std wheel bearing grease will eventually disolve plastic I'd only use the Delrin bushings with White Lithium Grease.
Good luck, please tell us what works for you, thanks!
Good luck, please tell us what works for you, thanks!