The oil flow starts at the rear cam bearing,goes through a tube to the center of the block,the tube is hidden by the lifter compartment cover.Then it flows into a block drillway,makes a 90 degree turn upward to the block deck surface.A small triangular opening in the head gasket directs the oil into the passenger side milddle head bolt drilling in the head.The oil then travels upwards a 1/2 inch past the non threaded part of the head bolt,then makes a 45 degree bend to one side and continues up to the head surface.That's where the oil is picked up by the rocker supply tube.
Non really mentioned clearly in GM repair manuals;there's a .062 restriction in the oil line,it varies in location.On many blocks it can be located under the 1/8 inch plug under the block center right.Can also be found under the center right side plug on some heads.Some call it a metered oil supply.The restriction can be located anywhere,just so long as it there .
Contary to wifes tales,at no point does the oil past by the center head bolt threads.
Crank the pump with a drill as mentioned above,or run the engine,if no oil,check the pipe under the side cover for sludge,or perhaps the pipe was left off. Use compressed air to check the flow from point to point.
