That project is for automatic thread cutting, I believe, and so it's kind of a subset of a CNC program, requiring a couple axes, and acceleration deceleration, a display and lots of button functions.
What I'm thinking of doing is MUCH simpler (or more primitive, depending on your point of view) --- simply replacing the change gears.
Cutting threads exactly as you would on a manual lathe, otherwise. No second axis, no acelertion deceleration factors, etc. You engage the half nut with the spindle and leadscrew already turning, just as you would with change gears. You feed the slide in as multiple passes, in the manual way.