Been there done that. I'd take the spindles to a machine shop with your nylon bushings and have him press out the old brass ones and press in the nylon ones so that they can be reamed to fit the king pins. Im pretty sure the thrust bearings are going to be needed to make the spindle fit correctly on the axle eyes regardless of the bushing materials used. I don't think there should be any play between the pin and the axle eyes, but I had a tiny bit in mine when I did it about 15 yrs ago. I've heard stories by some that the nylon bushings last longer than brass, and the other way around too! Since these trucks aren't being used like they used to be it shouldn't make a lot of difference. If I'm wrong, someone will correct me here. Mike