The item below was attached to the lathe bed casting, just to the right of the left-hand lead screw mount – it carried the switch box, I assume installed by the previous owner.

The part itself cannot be seen in the next picture, but here's the install location:

I don't know if he drilled and tapped the holes in the base himself, or if this is simply how the gearbox usually mounts. I've been unable to find any images online that answer this.
Can anyone help?