I have a Bridgeport Interact 1 Boss 6.1 control that I converted to Mach, it uses steppers like the original did but I gutted out all of the old stuff and fitted Geckos etc. My Lathe is big, can swing 290mm over the crosslide and 520mm over the beds, the turret,toolpost, cross slide and sadlle weigh in around 400Kg so it needs big motors. I have used AC Servo drives and motors and its working very well.
I am also converting another mill at the moment, a Beaver NC5 which is bigger than the Bridgeport. On this mill I have similar AC Servos and drives as the lathe (just a bit smaller).
Below is a pic of the Bridgeport after conversion, the Lathe as I got it and the only pics I have so far of the Beaver mill, first is thecabinet with the servo drives, second is the computer, breakouts, smoothstepper etc.
Hood