Having to make some assumption here.
1 The crank was properly machined.
2 The crank is not deformed in any way.
3 The main caps and block are not damaged in any way.
4 The shims your installing are the correct thickness.
This would lead me to believe the bearing are the cause, except for this:> I have plasti-gauged the journals at 1 position and seem to be in tolerance but know this motor would lock up if fully assembled.
Which would point me to think there might be an issue with the crank
If it were me, would try plasti-gauging all the journals at the 12,3,6 and 9 positions and record the measurements and see if there is a tight spot.