I've cleaned up the axle that came with the spindles and sure enough, the forged part number according to the GMwiki parts page confirms that it is a '57 axle. See part number in the photo. The spindles for 55-57 (and a few other years) are the same part, so no issues there if I decide to mate them with the '55 axle with thrust washers. The '57 assembly was good and solid, meaning it pivoted well and it had no play. I'll ponder this some more and maybe get a standard king pin kit (with thrust bearings) and use the entire assembly.
