I also have to figure out the size master cylinder I need. I will most likely mimic what was in a mid nineties chevy 3500 of a p30 motorhome. Some motorhomes used a dual hydrovac(what I've heard) or hydroboost which runs off of a power steering pump. or master cylinder. Remember, all this stuff was engineered to work for a specific application. I would not be very good at re-engineering which parts work with others to achieve proper braking.
