bandit controller retrofit

The 3 bottom wires on the drive boards, what do they have written ?
Do you have an old PC with parallel port?
If those wires are step/dir and GND, fire up the PC, wire some wires from parallel port to those 3 wires, move the machine!

To the left of the ribbon cable, are those optocouplers?
If yes, see what wires go to those optos inputs, those should be step, dir, and maybe enable, one is ground, and for testing you only need 1, the step pin, and if used the enable, but if the drives lock when powered on, then skip enable as they are enabled, so use a signal generator or parallel port, or a small crappy transformer that outputs 3 to 6V AC, should be enough to check if they work, and if they do, leave them on.
Be aware that some older drives use two inputs as step and have no dir at all, so steps on one pin turn the motor one direction, while steps on other pin move motor the other direction.
There are also "quadrature inputs" using steps on both pins, but 90 degrees between them, also no dir.
And as the last type, the 4 input ones, so when testing if the motor does not turn but just vibrates in place, check other pins, there should be 4 that cause the motor to vibrate.
All of those can be controlled by LinuxCNC, even through a parallel port, hence my hesitation to change the drives.
But if you think the time is more valuable, do change them.
And if the motors turn out to be 5 wire ones, they can be changed to bipolar, just require a bit of time and a soldering iron.
BTW, never ever remove the rotor from the stator on stepper motors, that will render them useless as they will de-magnetize.