[JSeery]

Good catch 51 Merc!! That needs to be checked to see if the horizonal passage is open or plugged. The horizonal passage that has the 7/16 Allen screw in it has to be open. The screw should not be there in your application! And of the two ports on the left in the diagram labeled 3/8 NPT, one should be plugged and the other used for the oil pressure sender. Does not matter which port you plug and which you use for the oil sender. The port on the right labeled oil return should be plugged as well (as it appears it already is).

I would guess the set screw is already removed and the issue is the one 3/8 port being plumbed to the sump. But it would sure be worth checking for the set screw just to be safe.