I've been away from the computer/Internet for 8 days and arrived back home last night.
As soon as I saw your "square metal do-hickey" I recognised it as being familiar.
It is
"the protrusion" used to correctly locate/mate the stator of the drive-motor with the alloy casting and it is ESSENTIAL.
That motor has high power-output. (Mine is 2.5kW!) And the same toque that is applied to the rotor is also applied to the stator - but in the reverse direction.
So that "do-hickey" is also there to stop the stator from turning as a result of this torque.
PS. This proves that photos aren't just good for enjoyment. They often trigger useful responses. (And I hope you'll see this reply as one of those.)
See Fig 8-50 here (Sorry it isn't clearer but it should suffice.):
