A special freeze plug recommended for modifying the oiling system on big blocks that are running a solid flat tappet or solid roller cam (never do this with a hydraulic cam.) Use one per engine. This is a quick, easy and almost free oil system modification.
This special freeze plug should be driven into the DRIVERS side oil galley from the rear to about 1 1/4" deep, or just past the cross drilled supply passage that runs across the back of the block, (the one that ends where the oil sending unit usually attaches.) This will cut off pressurized oil to the drivers side oil galley, preserving more oil for where it is needed, such as bearings, etc.
Unfortunately, the only way to cut off supply to the passenger side galley is to install a bushing in each lifter bore individually (you must have a knowledgeable machine shop do this) or by pressing in a brass tube and "dimpling" it to clear the lifters.