Hi Ian, sorry about taking time to get back to you but I am out of the UK with very little internet, I think the 500/700 is the difference between the standard which has a 500 mm long table and the LV version that has a longer table at 700 mm.
I have the LV machine, I found that to fit a ball screw on the "X" axis you will need to machine a space for the ball nut to fit in as it is all very tight for space, when I get back to the UK I will send you some photos.

Steve