[Kevin Kuehn]

Can you post a few pictures showing how the yoke and focus coil are positioned relative to the picture tube? A side, rear, and top view would be helpful. Tom mentions tilting the focus coil, but if you have wing nuts that allow forward/reward, as well as up/down, all those movements can affect neck shadow. The electron beam is basically looking down the barrel of the neck, and if it's not bent to center by all combined adjustments before it clears the bell of the tube you'll get a shadow.