I know I am late to this "Party" but, it seems you want to refit a manual Bridgeport. How are you going to deal with the backlash in your leadscrews? Are you going to refit the machine with ballscrews?
My first suggestion would be for you to watch for a purpose built CNC machine with a dead or old control. I just picked up a Supermax YCM-40 CNC knee mill for about scrap value. A fellow in my local metalworking club rescued a COMET CNC Knee mill from a scrap yard with an old Fanuc control, he sold off all the control boards and more than paid for the mill. He kept the yellow top Fanuc servo motors, along with their encoders and refitted the control with a Centroid/Ajax All in One DC control
I can recommend the Centroid All in One DC control. I just finished the refit of my CNC Knee Mill from a Mitutoyo Millstar III control to a Centroid All in One DC. I documented most of the conversion and even tried to go over the All in One DC subsystems on a dry erase board. You can find it on my YouTube channel, martyscncgarage. I have some pictures on my google photo album as well: https://goo.gl/photos/1AN1yNPp6GHyKkCn8
I estimate with the control, the encoders, reusing my servos, new TECO VFDs, cabinet, computer, nickel and dime stuff, I have about $4k into the retrofit. True closed loop industrial grade motion control system by a company that has been around a long time. My machine was in really nice shape, so I bit the bullet and am glad I did it.
My second choice would be to use DMM AC drives and possibly the Centroid OAK motion controller. I am looking at doing this combo for a Supermax YCM-40 I recently picked up.
My third choice would be the DMM AC drives/motors with the soon to be released ACORN Step/Dir motion controller from Centroid. Uses the SAME software as the software on the All in One DC. Outputs step and direction. You could use the DMM DYN2 which are less expensive than the Dyn4 using step and direction input. This is not a true closed loop system, the servo drive closes the loop however and is a better option than stepper motors. With ACORN, I will never go back to Mach. as long as it is around. It makes sense to buy the motion controller that is made by the same company as the software. No finger pointing...follow the AJAX forum on CNCZONE for more info and updates on ACORN. OR if you have any questions about All in One DC or OAK. The Centroid guys monitor it and try to answer questions.
If it were a smaller machine, the new line of brushless DC motors WITH drives built on from Teknic, Clearpath SDSK https://www.teknic.com/products/clea.../clearpath-sd/
would be another option.
(Now mind you, I don't have direct experience with DMM but I hope to try them out and I'll see about doing videos on that process too)
What exactly is your budget, what do you intend to do with the machine? DO YOU have some basic electrical/electronic skills?
My .02 on the subject.
Fun stuff, so much new technology out there....
Marty