You could do this Fattywagonman....
I havent seen how the piston pump oilers work, but the gear type has 3 galleries off the pump.
1 feeds the front main and rod, second feeds the cam, third goes up and over to the cross drilled chanel to feed the rocker box by external line and at the back end of the engine rear main
I suspect you could drill and plug the cam lube gallery and rout thios to an external filter and split this back to feed the cam and rocker box.
Or you could just use the factory internal bypass fuilter assembly fed from the rear main oil gallery ( If you don't this casting I have one I may end up scrapping, problem being I couldn't find a filter on the shelf for it and never realy persued it )
Doug
Doug