Those motors were originally CMC motors and typically were 24vdc to 48vdc and fitted with a Renco encoder.
If you measure the rpm at 12vdc you could extrapolate the maximum rpm for the typical range of 2000 to 2500 rpm.
The eight wires are the encoder, 6 for A,B,Z and the 3 complement of each plus two for power, usually 5v.
Those are nice gear boxes, BTW, and expensive $$$.
Al..