99% chance that it's a Yacht Specialties/Merriman unit. Good product, and my '88 model has YS steering.
(By the late 80's Edson finally won the "wheel wars" over their YS rival for sail boats, and continues onward to this day.)
Since you phrased the question as though a change to hydraulics is a forgone conclusion, I (and maybe a few others here) would be interested in your reasons. Such a change would be unusual on your model boat, IMHO.
Sidebar: In my area most of the factory wheel-optioned Cascade 36's and 42's that were built in the 60's/70's went with hydraulics because they used a bulkhead wheel arrangement. As the years went by most had leakage problems. Quite a mess, as years went by. Matter of fact I've seldom seen a "dry" one.
This changeover will provide some interesting engineering challenge when you add an AP or a wind vane, also, unless you plan to drive either of these directly off the rudder post.
From the "Devil's Advocate" point of view, I admit to seeing some nicely done hydraulics on boat over 45 feet or so, using systems that could drive an anchor windlass too.
:nerd:
Regards,
LB