Servos are just steppers with encoders. While there’s no provision directly on the Laserboard’s stepper drivers themselves to read the encoders, they will drive the stepper motor portion just fine and you can leave the encoders floating. Alternatively, if the machine doesn’t already have them you can get offboard servo drivers that read and respond to the encoder logic internally, then run those from the external driver ports on the Laserboard. Be warned though, servo drivers are generally fairly expensive.
What’s a bit more concerning though is many of the older BD machines had RF-excited tubes, which will take a bit more effort to get working than a more traditional LPSU design. With a few pictures of the internals of the unit, the laser power supply, tube, endstops, etc. we can determine further if it’ll be a good match.
In any case, this is going to be a much more involved conversion than your typical K40, so be prepared to make many modifications to the unit (no matter what direction you go in to convert it).