Joe. As I remember, the two way master cylinder ( which would be inside the hull) looked like it had a piston moved either right or left in a tube, and the hydraulic lines on either end of the tube went directly to the positioner ( in our case, outside the hull) and there was no pump.
As far as adapting it for a wet application, it seems to me that the addition of a hydraulic oil reservoir, pressurized to just over ambient, would be enough to keep the water out of the positioner.
You might leak a little oil into the water but clean hydraulic oil isn't a pollutant, and any leakage would be minimal.
As I was e-mailing Vance, I saw this in an old catalogue I had, and I will do a google search to see what I can find. Frank D.