Owen Dyneto wrote (COPIED FROM OTHER THREAD):
The restriction is to maintain a high oil pressure for the hydraulic lifters by minimizing the flow to the filter and back to the crankcase. Many folks leave this out when they replumb the system (for God knows what reasons) and ultimately face the consequences if they keep the car. Also, some folks when installing a filter on a car that didn't have one remove the pigtail from the lower to the upper galley and instead put the filter return there, assuming that the filter flow will suffice. Bad idea for two reasons, (1) the restrictor, and (2) if the filter plugs, you loose oil to the lifters.

The 356 engine is perhaps Packards best since the Twelve. I've owned a couple and have serviced several others. Lovely engine.