Originally Posted by
Discorde
The elevators would likely have been mounted on one axis, moving together.
Yes, I'm sure that was the case - as with, for example, the DC-3.
So perhaps it was only necessary to fit the lock on one side
I'd be surprised if it was, as that would imply that the torque tube was the only restraining force on the opposite elevator. The DC-3 certainly used a lock on each side, even though holding one elevator would in theory stop the other one moving.