Charles,
While it is possible to "mill" Rc58-62 hard steel, you are very unlikely to be happy with the results. In terms of the screw thread used on the sides, LMS is usually quite helpful about such things.
The traditional use of such vises is to hold small parts such that they can be moved from work station to station with their orientation and indexing intact. They are really not meant to be stand-alone workholding devices. You might find a 4 inch angle-lock type vise more generally useful. ???