conect 121 new toy

[m_c]

From what I remember, you can trace the step/dir control pins back to the original controller chip.

However, they are 80s technology, and I don't think it would be worth the hassle. Even a couple of the TB6600 drives should give an improvement in performance, and they can be had for less than £10 each. Combine those with a cheap BOB, and you've got all the major components covered.
The only thing is you'd need to ensure the 0-10V for the spindle speed is isolated, or upgrade the spindle drive to something that doesn't need an isolated speed control.