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.