the main problem with running a power 'box with no pressure is that the valve body has way too much movement before it will move the pitman arm. just rock the steering and observe the input joint moving in and out with the engine not running. that is what exposes the valves internally to operate the power steering.
but I don't see any reason not to strip the power steering box, remove the piston for less drag and replace the centering springs for calibrated spacers. then fill with standard steering box oil and fit plugs in the pipe connectors.
but if you replaced the centering springs for heavier springs that would in effect make a correctly working power steering unit heavier. a much better way than just reducing pump pressure as reducing pressure requires more movement in the input shaft increasing play again.
