John Rigg built a replica of the Krell Lock and has it on display in his Robot Hut in Spokane.
http://www.robothut.robotnut.com/krellock.html
Rigg's version is "based on blueprints" and therefore not identical to the screenused item.
The Krell Lab has two Locks visible at the same time, one inside and one outside the door.
The outside lock is pointed edge-on towards the door in scenes set out in the corridor outside the lab
Note also that the outside lock is tilted up so that its right edge is vertical.
In this photo taken during production, the outside lock has been rotated towards the lab door.
The Krell Lab blueprints (from the Cinefantastique double issue on Forbidden Planet) may provide some scaling information.