Lincoln Zephyr motors 36/37 have only 2 oil holes on top of the block / bellhousing at the rear, they are both oil supply holes, one for oil pressure gauge the other to supply oil to the filter, this filter is only a By-Pass filter. The main oil supply is inside the motor, and is unfiltered. The return oil from the Filter is piped straight into the side of the sump. All filters have a built in Restrictor in the center pipe. On L/Z motors 38 onward all have Hydraulic Lifters, the bellhousing has a third oil hole lower down beneath the other two supply holes. "Some very early 38 L/Z motors dont have this third hole." This third hole has the oil return pipe from the filter connected to it on these models and not to the sump. This supplies Filtered Oil to the Lifters. Lifters love filtered oil. Inside the valley under the Inlet Manofold at the rear under a 1 inch. screw out plug is a 12 LB. oil regulating valve, it is screwed in too, it regulates the oil flow to the lifters under cold start conditions and if the filter gets clogged This valve may be missing or has been replaced with a plug on Ralphsnof49 L/Z motor. This could reduce oil flow to lifters or allow loss of oil pressure, depending whether its missing or plugged, especially if the 1 inch. plug above it has been left out as well. This 12 LB. regulating valve only supplies oil to the lifters during a cold start, for about 20 secs. until the filter has filled up, because the filter drains back when parked up, once the filter has filled the oil flows over the 12LB. valve and shuts it down and the oil flows to the right hand lifters, it already has flowed to the left hand lifters on the way to the valve.The oil galleries are complex. So the pipe work has to be right and the correct valves in place. there is also a different relief valve at the front of the block, this distributes any oil left after passing thru. the lifters to lubricate the Cam gear.