It all depends on what is reusable.
What voltage is the existing power supply?
Also, what may skew your choices is do the existing switches/sensors use 5V or 24V?
(i've got no experience of emco stuff, but I'd guess on that size of machine they'll be 5V)

As Irving mentions, you'll want to find out what motors are already fitted. Provided they're 2phase, reusing them won't be an issue, although you may want to consider upgrading them at some point, as more modern motors will have better performance.

Also, how is the spindle powered/controlled?

There are other options than a SS (if you do go SS, get the ESS to avoid usb problems), but you have to be careful to check they support lathe threading

That all might sound a bit daunting, but if you sit down, figure out what you've got (spindle/steppers/sensors), what is needed to power/drive it, and how you'd like to control it, we can point you in the right direction.