Take a look at MachMotion equipment;
www.machmotion.com. They build CNC machines and sell retrofit kits. The mill you have is a fairly solid mill as I recall. If the motors and amps are OK, you can install a controller and control panel. You will need newer differential encoders, but the limit switches and ref switches are probably good to go. Machmotion can advise you on a VFD, as they sell several different sizes.
The Bandit control is from the early 1980's, and was a low end control then. Also, you need to spec out the amps, to know if they will work with a newer controller. To end up with a reliable machine, I would go with an external controller, and bypass the parallel port type of installation.