Just looked through the SeaStar system that I have. My dad bought it for a sterndrive, so the cylinder will not work and will get sold off to recoup costs.

Helm is a HH5271-3. Hoses are either 16 or 18 feet, 5/16" ID, part number 136329. Looks like I need the HC5345 cylinder for the Yamaha. Should be a significant upgrade from my current Baystar setup.