Thanks Rick for the wonderful write up, and I would try this with my FE and FE2 screens, since I desire to MF my older Nikkors and surely this will help.
It is interesting that the ~1mm on each side, thus making the cradle missing the screen completely did not matter... and yes you are right, perhaps the F6 screen would work better.
As to calibration, my thoughts are, from the manufacturing perspective, it would be foolish to change the thickness and calibration of the focusing screen between camera models, as that would entail resetting up the manufacturing process each time a screen is made for different camera. So I do not expect there to be a need to calibrate as long as the screens are Nikon. But that is only a conjecture...