Just to clarify the history of your machines Jazz, was this kit removed by you for a reason , or had that happened before you got them?
The machine was cheap enough and I am told operates manually , so I wont mind spending a couple of hundred to see a modern computer driving it . I dont see why I would alter the spindle drive provided it is working OK

Are you saying that at worst a couple of Stepper drivers and a modern BoB should be sufficient to get it going