I had wondered whether redirecting it all to the head would flood the cam cover, so have thought of using the gauge I intend fitting on the head with a bypass to adjust the flow, re-redirecting any excess back to the block. Reusing the original tapping.
That sounds like a good plan. As I understand it the rocker arm line does restrict flow (by the size of the opening in the fitting). The only other caveat is that the factory design allows for filter neglect. Should it become completely clogged the rocker arm line would still flow through the other side of the T. With your design the filter must be looked after diligently.
