If you have a low oil pressure problem at idle, the shim trick won't help. It only raises the treshold pressure for bleeding out EXCESSIVE pressure, i.e. off-idle. It only raises the maximum oil pressure limit, it does nothing for the low pressure. If you raise your oil pressure, you need to know what other things it may cause, like 100% oil filter bypass (no filtration at all) or some other harmful side effects. And you would still have low oil pressure at idle.
IF that is your problem, then I would try to find out what the root cause is. Without knowing this engine, I can only give a generic best guess and say worn bearings. Maybe oil pickup tube getting air from somewhere, a loose fitting tube could do that. It would also aerate the oil.
