That stuff is getting hard to find. Try posting a free “Wanted” ad on the classified board here. Run searches on E-bay and Craigslist too. The hydroplane steering wheels mount to the surface of the dashboard and the steering cable drum is above surface between the steering wheel and the dash. You may also want to seek out a spring-loaded (dead man’s) remote throttle. If you rig up a lanyard to cut the motor if you fall out, or otherwise need to shut down instantly, you probably won’t need the dead man’s throttle.
Dave