Hi Michael,
If these are the lead screws that came with the machine then I would suggest that they are not suitable due the backlash. You would have to check to see if they are a buttress style thread, if so then you to change for ballscrews. The Super Major looks the same as my mill so I can provide some guidance and explain how I converted mine.
I have converted mine to a 3 phase motor and VFD, kept the gearbox and can get 3000rpm which help with the smaller cutters. I could get more rpm but I don't want to explode the gearbox!
Do you use CAD, if so what CAD system?
Regards
Simon