Hallo Franz,

I would start at YASKAWA. The company is still existing. And the question is how to connect a controller/converter for GCode to the motor control units. Typically they change the protocols/standards not so often. Heidenhain seems to support YASKAWA also. Fanuc or Siemens? I read also something about YASKAWA servos in the LinuxCNC/EMC2 forum. Ich hab mal ne Käsefräse gebaut und damit angesteuert. To get the axes run is possible I thing - Control the tool change is another thing. A new software for 5 Axis milling isn't free available and has to be configured to the special machine.
Who make the maintenance of the machine. Maybe he can help.

In general - what a desaster:-(

Karsten

p.s.: google for yaskawa sgda-08as - you will find the a pdf of the controller family S.398 the spec for I/O signals - so a specialist can give you a tip:-)