Still stumped; can't get 2 of the 6 bolts to catch on the threads. Removed the cover today; looked for any interference, and found none. Checked the cover for warpage with a straight edge across the three towers in the long direction, and it is flat. Even stood on the cover (180 lbs) as I tried to tighten the bolts with no effect. I'm done, but 4 out of 6 ain't bad.
Mark