I have done two of these with the emc2 system. If you are interested in saving yourself a ton of work - my advice is to simply use the pre-existing stepper motors that are on the machine. Buy gecko 203v stepper drivers. You can use a 60v or 70v dc power supply at 13 amps.
If you do not have 3-phase power, you can run the spindle off a teco-fm-50 VFD that accepts simple 230v single phase.
This is a quick and simple solution that takes me about 40 hours of labor to have the machine up, running and cutting.
(here is a link for someone else who has done the same procedure but he uses mach-3)
Bridgeport Series II CNC Gecko/Mach3 Conversion | The Steampunk Workshop
WWW.RAIDGEAR.NET - FFC cables, foam headset replacement parts, and other gadgets.