I'm retrofitting my Sabre 408 with the Masso G3 controller ($900 with accessories and shipping) and 12NM NEMA 34 closed loop steppers ($180 each x3), using the existing 74v power supply. To get NEMA 34's to work you'll need to machine new mount plates (x3) and figure out a way to attach the 11mm bore pulleys to the 15mm (or whatever you get) NEMA 34 shaft. I'm trying to find replacement pulleys (just starting that process, so nothing to report yet).