worried....... a little
This sounds like a real puzzle. I've been trying to imagine what scenario could create a bind at only 30' of rotation (10:30 - 12:00).
You've said the lifters were out so they can't be affecting anything.
The distributor/gear is not engaged so it shouldn't be a factor.
The problem exists whether or not the cam sprocket is attached - so it isn't the problem.
The only way I can imagine such a thing is if you've got 2 conditions working together.
You said the cam bearings were used. I'm no expert but I could imagine that the bearings might not wear evenly and have an out of round shape. If that is true and your camshaft does have a bend in it, - it could create a condition where the cam gets tighter at certain positions.
Just a wild guess on my part.