Join Date: Jun 2016
Location: Orange County, CA
Chassis: Crown Supercoach II (rear engine)
Engine: Detroit 6V92TAC, DDEC 2, Jake brake, Allison HT740
Rated Cap: 37,400 lbs GVWR
My bus has a Webster KB power steering pump that also supplies the radiator fan's Webster YC motor. I don't have a pressure gauge on the PS circuit, but the high-pressure gauge for the radiator fan motor shows up to 1500 PSI at 2100 RPM engine speed, so I guess the Ross TAS65 steering box also takes about the same working pressure. If you know exactly what make and model of PS box you have, you can look up its specs online to find out its working pressure and flow rate.
It surprises me that you have steel lines for the PS box. My bus has R2-10 hydraulic hose from the pump to the PS box and R2-12 to the fan motor, and after 29 years there's not a drop of leakage. It will be a lot easier for you to buy a few hundred bucks of R2 hose instead of dealing with several sections of pipe and all the fittings, any one of which can be a potential leak.