The internet is great!! I was able to find the Yaskawa documentation for the X and Z Servo Motors and Optical Encoders. The good news is these are simple DC Servo Motors rated at mild 400W Continuous and 2000W Peak. Even better is optical encoders are old school digital quadrature with 500 p/rev. (looking at the datasheet, I am not sure if this means 500cpr / 2000ppr or 125cpr / 500ppr, I am hoping for 500cpr / 2000ppr) The output voltage is a collector pulled up to 12volts, so I should be able to convert this to TTL levels. (not bad for 1979)
In theory, I should be able to drive these stock servos and stock encoders with a simple gecko, viper or CNCDrive
Attached are the datasheets for Servos and Encoders