Looks a good bit like a holder for a boring bar. A number of lathes, Myford, Emco, have t-slotted cross-slide tables for mounting all sorts of things like this. Unless I'm mistaken the knurled collar will let you set the height. It also looks like inside the small hole on the top casting you've got a split collet that will tighten up a 3/4 inch boring bar (or whatever the hole diameter is).