Fomoco used plastic king pin bushings in F-500-700 trucks with the 7000 lbs front axle in the 1970's.They were short lived in medium truck use ,lasting about 6000 miles in school bus service.The normal steel backed soft metal (brass, bronze?) bushings lasted much longer.I can't say from actual experience how long a nylon bushings would last in a light truck use.You could install them ,and let us know if they last.
