Having read through this, my comments.
Preload on the bearings will not affect this. The critical dimensions are the width of the ends of the wishbone and the depths of the threads on either end of the fulcrum pin. So one of these is wrong if the nuts are really bottomed out on the threads.
There should be a big thick washer under each nut which sits flush on the outside of the wishbone and lets you tighten the nut down. Not having this in place will shorten your threads by double the thickness of the washer; easily 1/4". Make sure that the ID of your washer is big enough that slides freely on the unthreaded section of the shaft.
With washers installed, if you still have the problem, I would inspect the threads and ensure that the nuts are really going on all the way; this is likely to be the cause of your problem.
AS shown above there should be a strong washer under the nuts for the shock absorber that is bigger in OD than the rubber bush to make it impossible for the shock absorber to move laterally.