I am renovating a Bridgeport using Electrocraft motors, one is a 4030. This is a high end setup particularly well suited for CNC. I'm using Electrocraft drives which can take step and direction. EMC, Mach2 or Turbocnc will all work with this setup, and you avoid spending $700 on an interface card. Suggest you go with a breakout board for the parallel port.
You might want to check out the project logs for mills, there is mine and one that actually a conversion, which sounds like what you are doing. You can find it here:
http://www.cnczone.com/forums/vertical_mill_lathe_project_log/