its possible it can be retrofited with steppers, I am not sure if thats the best way to go about it or not ( I just really dont know). You might even be able to use the motors on it and just add servo drives, possibly encoders and a breakout board and then use Mach3.
I would post this in the Bridgeport section. I am sure others have retro this machine before and you can read about how they did it, plus get feedback on how they think they should have, or if it worked out.
Having some numbers off the motors and pics of the controlls (inside the controller) they could help get a idea of cost and tell you exactly what you need.
Either way its possible to retro the machine even if you have to start from scratch. Your already ahead of the game because all the machnical parts are there. The electrical part is not bad, its just a mater of how much.