Thinking about this for a day, it was on a friends truck where I was able to just ...
tighten it down.
"Maybe Steve put the extra washers in when he rebuilt the bar and not tighten it all the way to the stop?" On my own truck, the assembly went according to the instructions. No slop yet at ~30,000 mi since install.
On another owners pickup, I could only get the larger washer in and it would not bottom out. 5,000 mi. later I was able to finish the tightening of the "plug". I took it apart 3 times trying to figure out what I had done wrong during initial assembly, but found nothing amiss. It is working great for him at this point.