The head on mine is different than yours also. It has the variable speed pulleys. There were M codes that basically run the speed adjustment from one end to the other with an air motor in high and low gear ranges. This provided 4 separate ranges and the spindle inverter varied the speed with in them.
Example:
M41....60-165
M42....166-499
M43....280-1,469
M44....1,470-4,640
The inverter speed control is analog 0-10v also. I plan on doing away with the PLC. It was setup to handle the few M codes. The Original control was setup to do a MST transfer function to the PLC.
Darek