I did something similar to your original question designing a single control box that could be moved to multiple specialized machines. The box has switched 120V outputs to control the spindle and a worklight, stepper motor outputs using 4-pin molex connectors (the same connectors used internally on PCs to supply power to disk drives), and connections to the motor power supply.
As I moved the box from one machine to another, I made a tiny, insignificant change to the motor parameters and re-flashed the GREX. This kept the GREX in calibration for each machine.
I have since purchased a number of used GREX controllers and drives and built a separate box for each machine. Pictures are attached.