This mill is from the early days of CNC, back before manufacturers knew what they could get away with. Hence the mechanical elements are extremely precise. The electronics, on the other hand, are so old that we declare them a loss. Rough game plan
- Strip the mill down
- Clean it up and lubricate it
- Replace necessary mechanical elements
- Build up new electronics, test extensively and integrate
- Software for CAM and control
The existing drive (stepper) motors may or may not be restorable and some of the gears need to be replaced. They are small gear-drive units (are they actually servos rather than steppers?), with associated extra hardware. It could be much simpler to replace them with larger direct-drive steppers. A package of steppers plus Gecko drive can be had from cncrouterparts for $519.
Gecko Drive G540 4 axis controller — $299, or see package with steppers for $519 above.
Pycam works for arbitrary shapes, but takes a while. There are other ways, including just writing the g-code by hand or designing your part in python, generating both openscad and g-code from the same source code.
In general, open source g-code generation tools for subtractive milling are not as complete or mature as those for 3D printing. Yet.