Charles,
I went back and re-read all of your posts. It seems to me that you've ruled out lifters, since you stated that as you adjust them you bring them to individual clatter, then silence them by adjustment, but the knock remains consistent as you adjust lifters.
One thing that you have not shared is the history of this engine. You mention "...when I put it in (the truck)..." that initial driving was limited to your long driveway, but you haven't said anything about the engine being new, old or in between. Can you share some details about when it was last apart, who put it together and if a machine shop or rebuilder was involved?