oil pump output check?

Well, in that case you’d better look into improving your drainage as shown in this pick. You need to put a similar fitting into the back of the timing chest then connect them up with some hose.

As mentioned already, the rocker shafts are installed to deliberately restrict the flow. Turning them 180 degrees will increase the flow.

However, I don’t know how to predict what effect this will have on the oil supply to the bottom end, I’d be concerned about starving the big ends of flow and / or pressure...