If you search around long enough on the internet you'll find links to the setup you have, where you are driving the machine by sending signals to the stepper drives from a parallel port.
My machine I gave up on that and replaced the stepper motors with modern ones (simple unbolt and replace - same form factor Nema 23 and 1/4" shaft). I also replaced all the legacy electronics - while intriguing, they are just not useful in a practical sense and it was easier (faster) for me to replace them.
Long story short - I don't know where the original turret motor control was located, but it was only maybe 2 relays (forward and reverse/hold at half voltage)..
My turret is now controlled by Linuxcnc through a modified component, though you could also just use the original control as well.
Mike