My view is that the rocker feed comes after the filter. My reasoning is that any restriction after the T off will send more oil to the rockers, and this continuing cycle will result in an ever gradually increasing volume of oil doing a sump, pump, rocker, sump path rather than a sump, pump, tank (with a bleed to the rockers). The result is less oil in the tank, more in the sump, baffled, confused and covered in oil syndrome.
Doing the plumbing is easier, so it's a matter of inserting the filter of your choice in the return line from the pump. Plenty of examples on the Forum.
Swarfy.