The Morse rack and pinion steering was preferred on many boats as it provides "no feedback" to the helm, that is you can take your hands off the wheel and the helm stays on course and doesn't veer from torque. For larger boats where you may not have hands on the wheel all the time like you would on smaller boats, this was the feature that sold these units...in the previous century.
The length may be heat stamped into the jacket at one or both ends, typically at the tiller end. The rack is part of the cable, and replacement will include the rack and cable. The cable length will be the jacket length + 18" then rounded up to the next full ft.
Rather than have a diver take a look, try disconnecting the tiller arm from the cable end and see how free the rudder is.
Your top choice in hydraulic will be Sea Star formerly Teleflex. Very reliable, my last boat was 20 yrs old when I got it, 30 when I sold it, still had fully functional original Sea Star hydraulic.
If you want the really good stuff Sea Star Capilano is the "commercial" grade steering that includes variable ratio steering
Morse was purchased by Teleflex now Sea Star (Dometic) long ago, you will find the replacement Morse Rack and Cable listed as a Sea Star part, for example:
SeaStar Solutions