Rye CNC Router upgrade (w Picture) - Agors

[m_c]

If the servos have only be running of 70VDC, then they won't have been running at the full speed anyway (for electric motors, voltage = speed, current = torque).

Those leadshine drives do look like they'd be capable. CNC Drive also do suitable drives (http://cncdrive.com/DG4S_08020.html for 80VDC/20A version).
The key to using those will be making sure the encoders are suitable. You need quadrature encoders, not resolvers which your machine might just be old enough to have.
For modern servo drives, the tacho output from the motor is generally not needed.

Z axis you can do however you want. It's not likely to have a lot of travel, or need to move that fast, so a suitably geared Nema 23/4 motor is likely to be a good option. You will however still need a driver for it.

You'll also need a breakout board of some form, but I would advise against using a parallel port, as it won't be fast enough to get the maximum benefit from the servos.