As a serial interface you cannot run it with Mach3. You would have to dive into the controll wiring and figure out HOW the drives interact with the controller.
Then you need to pick a NEW controller that runs in Mach3 and wire IT to your existing drivers PLUS add in all the I/O such as limits and home switches and ANY OTHER functions that are used such as spindle speed/on/off Vaccume or coolant, etc.
Warning IF you are not well versed in control wiring it may be best left alone. An old WORKING machine is always better than a BETTER NEW Controls machine that is broken and does not work.
NOW IF you get it all working control wise be AWARE that your OLD g code programs MAY NOT run in mach3 and you will have to reprogram ALL the old programs into Mach3 GCODE.
Just a thought, (;-) TP