Thanks for the replies.

The biggest problem I have is that
a)the small holes in the box aren't threaded (I've got a Klien tapper, so it's possible, just time consuming), and
b)most of the boxes are rivet mounted on steel straps mounted between joists - so I'd have to punch / grind out the rivets and then find a way to mount the new box.

Oh well... I guess this is the "artistic" part of our job, huh? [Linked Image]