Thanks to all for your thoughts on this. I'm getting the impression that pinion preload leans a little more to art than science. Tom, I went back into the archives (which I should have done before I posted this) and found a wealth of information you have posted over the years on this and other rear end issues. I loved your story about the one you rebuilt where someone had tightened the preload nut so tight they had frozen the bearing and the entire pinion assembly had been spinning in the banjo housing for many years. After the initial heat-up I guess it got enough lube to keep working although a little noisy.
Bob