These were very common on the surplus market around 20 yrs ago.
Many were without the Tach, which is the rear two connections.
You may be able to remove the tach and put an encoder on it.
I believe they were either 24vdc or 48vdc, they are probably OK up to at least 3000rpm.
If you apply a known voltage and record the RPM the max voltage would be pro-rated accordingly.
I still have a couple kicking around somewhere.
Al.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.